I did our estate plan on my own, using a variety of templates and documents (not fill-in-the-form software or websites). The attorneys may or may not approve of doing this on a DIY basis, but so far all of my documents have passed muster when needed, even when being reviewed by other attorneys (for example, I've used Trust Certifications successfully, durable and limited powers of attorney, and so on). Also, it's worth noting that attorneys also use templates; rarely is a document written from scratch by them. You can use the same templates for your state. Otherwise you're largely paying for a paralegal to modify a template you could do yourself.
I don't mean any of this to detract from the services attorneys provide. I did a LOT of reading on the subject beforehand, checking out many books from the library written by estate planning attorneys. I doubt I could have come up with a reasonable "DIY" plan on my own without that, using just the more amateurish fill-in-the-form stuff. I probably would not have undertaken this on my own without doing so much research to the point I felt comfortable taking it on.
Also, for just a little bit of a contrary perspective, courts will generally give broad leeway to estate plans which at least meet some basic criteria. It's unlikely a properly executed Trust or estate plan is going to be declared invalid unless there are some pretty glaring problems. YMMV.
Also for comparison, when I've tried most of the templates offered in typical consumer software or online, I ended up with an estate plan that was maybe 20-30 pages in total. After doing a more heavyweight (and I'd say far more complete and professional approach), I ended up with an estate plan somewhere around 120 pages. This passes the "thud" test, at least, much better (usually a well-thought out estate plan will make a "thud" when tossed on a desk, not float down from its lightness.
I'd say like most things, if you're willing to invest the time learning, it's worthwhile to do this on your own. It has the added advantages of:
a) Knowing if you're being "sold" things or being taken down a wrong path from an unscrupulous attorney, or one who really doesn't know what they're doing. You might be surprised just how many "professionals" there are that claim to know what they are doing in estate planning, but really don't. I imagine some of the attorneys on this site would agree here. (See threads on "Certified Financial Planners" for a similar discussion of professionals who can lead you astray).
b) The knowledge you gain will continue to serve you in many ways, for the rest of your life. You'll make better, informed decisions along the way. For example, I can make financial decisions even after my estate plan has been executed, knowing the tax implications, legal implications, how to set up ownership of accounts and property, beneficiary decisions, insurance decisions, and so on.
c) You will be competent to make changes to your plan over time, as your life situation changes (kids, deaths, marriages, divorces, family dynamics, changes in giving philosophy, whatever). Might as well make the investment up front to learn this, otherwise you'll likely be paying an attorney every time you want to amend your plan. There are some really great books on the subject matter that will teach you everything you need to know. And even if you do end up hiring an attorney, the knowledge will serve you well.
So please at least do a little reading from a good book, then you can make the choice that's best for you. Good luck!