I should clarify that the line I really use is that "I give freely but I don't work for cheap". Most of what I make is for donation, and I make them because I enjoy making them. I believe the standard in donation quilts is to do them exactly the same as if they were for the person you most love in the world. There is less personalization because I don't know who they are going to, but workmanship and materials are otherwise indistinguishable.
I've done quilting/sewing things for pay and there is absolutely zero wrong with that, it's just not what I want to do and my first reply wasn't very helpful in that regards. I just don't want to work on other people's deadlines or with what they want as opposed to what I want to do, so it still remains to decide what you feel is reasonable.
I do, however (and have for some time) put a value on my time of that $15 per hour. It started when I put in the commute time to get to my job, 2 hours a day in traffic (1 hour each way) really brought down my hourly wage! It helps clarify things like if I forgot a coupon I wanted to use, it is worth $7.50 (round trip) to go back and get a dollar off coupon? (answer is generally no) It does give you a different perspective from, "oh I have all day/all this time available" when it you phrase it as "what am I going to do with my $120 dollar day".
I'm currently putting together a UFO that I will be returning to it's owner. I'm doing it because I find it fun. Again, most of my work is for donation and in this case I'm donating time to someone else and it's all good. That's what I'm going to do with my day today -- that and some house cleaning.