many USCF races offer cash prizes. the race series I promote (an low key but USCF-permitted training series) gave out $9000 cash in 6 days of racing as well as about 2000 lbs of PowerBar drink mix, Olbas stuff, about $600 in gift certs to a local shop, and trophies. we've given away other things like framesets, high end wheels, and one year electronic goodies (XBOX, MP3 player, digi cam, etc).
however, I don't think many people race for money at the hobby level. to make back the $3000-5000 you spend on a bike, maybe $1000-2000 on entry fees a year, gas, food, tires, clothing and other gear, time to train... well my best year I got about $200 in prize money. lol. so you get to buy gas or food on the way home. that's about it.
for us mortals racing is about having fun.
a friend of mine is a top level woman racer (raced at the Elite level this year, did First Union, etc) and she got nothing but some entry fees and one jersey and one pair of shorts. and I wondered why she didn't train in her sponsors colors. she bought her own bike and paid her own way to races. and she had to compete against the top women in the world.