Average sized square bales of brome hay in this area are typically $3-5 per bale, depending on whether you can pick them up or need to have them delivered.
Rounds bales of brome I have found to run anywhere from $25-40 per bale. I paid $40 for the last 2 I bought and these were 1600lb bales. My 2 boys go through about 2 round bales per month.
Note that I don't have a round bale feeder, so they do waste some. They prefer square bales, but I have no where to store them so rounds are just easier for me, plus that way they can free feed.