I'd suggest you give the kids general information on how much you're willing to spend on college. We told our kids that we would pay for 4 years at a state school: Tuition and fees, dorm room and meal plan. OR Tuition and fees for the university 30 minutes down the road and a car. We told them we would not fund extra semesters beyond the 4 years or private /out-of-state schools. And with those ideas in mind, we started visiting schools.
At the same time, be flexible with your guidelines. For example, when we told our oldest that we'd pay the above expenses, we didn't know that all nursing majors must attend a mandatory summer school between the sophomore and junior year. We'd said earlier we weren't willing to pay for summer school, but we meant we weren't willing to pay extra tuition so she could have light semesters or because she'd failed a class. This was different, and we paid it. Also, when we started this process, we didn't realize that her university included books in the tuition. These are the things that vary from school to school, and you can't really know what to expect until you and the student choose the school.
Junior year is the perfect time to visit colleges, and with both of our kids we visited LOTS. We talked and compared the schools, money being one important piece of the puzzle. We helped them see the things that really mattered; for example, our youngest was temporarily enchanted with one certain school because of its lovely setting and fantastic dorms -- but when we pointed out that her choice of majors would be greatly limited, she began to put things into priority. My oldest was temporarily interested in an out-of-state school with a big name and a big football program -- but when she began to investigate details, and she learned that it's a big Greek school, she decided that just wasn't her thing. Kids can't make informed decisions if they don't visit and talk and discuss! Yet I see so many of my high school students make their college choice based upon very superficial items; those are the students who either leave college altogether or transfer (and transferring is an expensive option in terms of money, trouble, and time-to-graduation).
Making the actual decision is difficult, and I'm not sure it isn't more difficult when your kid is the "high honors student" for whom so many options are available. You have to make decisions without knowing final costs and scholarship possibilities. Note: Most scholarships are not school-specific, so don't hold out too long with those hopes. My oldest fell in love with two schools and had a hard time choosing between them. I really think either one would've served her well, but she LOVES the school she chose and has had a great two years thusfar.
What the student plans to study comes into consideration too. For example, my oldest is studying nursing; thus, her degree -- whether it's from State U or Private-Snooty-Schools-R-Us -- will never get her a job. Rather, the degree will allow her to sit for the exam that will allow her to be licensed by the state, and THAT will get her a job. In contrast, if one of your kids is interested in politics, he or she may need to attend THE SCHOOL. In general, I'm not into paying for a prestigious university.
In general, the more guidance you provide, the better choice they (and you) can make. 18 year olds often don't have a clue about what they want to do and how they should best spend your hard-earned college money. My girls are good students, serious about college -- but the oldest definitely benefited from massive amounts of guidance in making her decisions, and we're still going through that process with the youngest.
Finally, don't worry too much about the possibility of a kid frittering away your hard-earned money. In reality, this should never happen. Yeah, we all know kids who've done it -- for example, my high school boyfriend did it. He had top grades in high school and plenty of ability, yet his mother had babied him and supervised his homework every day (yes, even when he was a senior!). She'd sit him down at the table with a plate of cookies and make sure he did all his work every day. No surprise that he had no SELF-discipline, and out on his own, he fell on his face. Details vary, but most often the student who "isn't going to make it" has shown signs of this ahead of time.
First, the kid you're sending away to school is the same one who's been living with you for 18 years. In your heart of hearts, you know whether he's college material, you know whether he's serious about this opportunity, and you know whether the school he's choosing is a good fit. If you have any reservations, SAY NO. If you fear your student isn't emotionally or academically ready, insist upon a year at community college. Second, every student should be on the semester plan. That is, you pay for the first semester, and upon receipt of good grades, you pay for the second semester. If the good grades aren't forthcoming, you stop and reconsider your choices. Does the student need to change schools and come home to live? Is having a car on campus too much of a distraction? Did he just not study enough? If things don't go well that first semester, MAKE CHANGES. A student might fool one semester, but if you allow it to go on and on, it's on you!
And if you end up with extra money? That's an individual decision that you have to make for each student. In our case, our oldest ended up with some very nice scholarships . . . and we bought her a car (with the money we didn't spend on tuition). With student nursing coming up in the fall, this was a real need, and we all felt good about the choice. For another student, this money might've gone to cover the extra expenses of a semester abroad or graduate school or an apartment off campus.