Welp, I'm going to toss aside judgements of "having too much when others don't have enough" because that's a totally different issue.

You have money to spend on yourself. The LBS has been really, really supportive, right? Getting a nice bike from them would do them good, too. There isn't a cheaper alternative that will do just as well - that's what makes a purchase unreasonable in my book. This could also -and I'm not just rationalizing - be cheaper than medical equipment/treatments you won't need later because you've got the right fitness equipment now.

I'd make sure I really *could* afford it... but then I'd do it. (I "needed" that blender, myself - *nothing* does the same thing!)