Fishpick,
Difficult question to answer. The four guys I know that cut hay try and look at acreage yield on a yearly basis. The yearly count will depend on rain, temp., improvments to the field, etc.
If an acre will produce 4-6 rounds, 3-4 times a year, that pretty good. In this part of Georgia, a lot of guys have been lucky to get two cuttings and only harvest 2-3 bales per acre this year. Typically, the guys that have the gear to cut and bale hay usually also keep cattle. This means that whatever hay they cut will first go to feed their livestock and IF there is any spare, they'll sell it. This puts a lot of small acreage horse people (me) at the bottom of the totem pole for good quality hay.
Robj is right. I'd be suspicious of a $15 round bale. If it's good quality, fresh baled hay, anything under $30 means the guy is losing money. I've seen rounds that have been sitting out for a year and that are made up of mostly weeds that go for $10-15 but I wouldn't feed that stuff to a goat!
Marcussen, good luck with your search. Same to anyone else looking for quality hay this year. It's going to be rough!!