The answer will be what your life goals are and how much you can spend and not delay / destroy them.
For example, If my goal is to retire by age 40, have 50 years of cash equivalent at a 4% withdrawal rate, including 3% inflation and an average 7% return on investment, that will define what I can do right now. If I can buy a new car, or put in a pool, or whatever, and not hurt that goal (and all supporting goals), then awesome. If not, I figure something else out.
Of course if you haven't gotten that far yet (I haven't), I look at it as can I justify the investment in my home. I can't speak for your area but a garage is a practical necessity to get serious interest in a house. If you spend $7.5k for a 2.5 car garage, and enjoy that utility for a number of years, and can get a reasonable amount of that investment back, I don't see a problem with that (but I also use my garage for lots of money saving activities so it's easy for me to justify).
On the other hand there is a laughable trend around here where people buy sheds for 5,6,8k. I mean, these are just things to store lawn mowers and potting soil. I don't know about you but everyone built their own sheds when I was a kid, having one dropped off at your house wasn't an option. Anyway, I don't think you'd get one dime of that investment back on a home sale.