alfalfa is ok for 7 mos and younger (and can be purchased by the bale at feed stores)... rabbits of any age can have ANY type of horse-quality grass hay. with "cereal" type hays like oat and wheat, you need to pick out the oats or w/e as the extra carbs are no good for bunnies.
feed store hay is usually actually fresher than the stuff at pet stores... and pet store hay is around $3 per lb vs feed store hay being about $1 for 7-8 lbs.
if you want to buy hay online, it's going to be a lot pricier than a feed store... however, this site has the best prices I've seen as far as ordering hay online -
http://www.sierravalleyhay.com/Orders.html ... I went through them because my stupid bunnies are obscenely picky and only like oat and alfalfa and are just about too old for alfalfa... though I also ordered a bale of 80%/20% orchard/alfalfa to see if they'll eat that. I ordered the hay on 12/21 and it arrived on 12/27, which is pretty darn fast considering there was a weekend and a holiday in there.
it only cost $31.95 for 20 lbs of oat hay (*including* shipping), which is a hell of a lot better than the obscene price of $26.99 for 9 lbs that oxbow charges (and that didn't involve any shipping fees since the feed store ordered it for me), and also much better than ordering from binky bunny since their shipping prices are horrendous. I haven't opened the hay yet (it's still on the porch until I rearrange stuff in just a bit to make room for it), but I'll report back on the quality. it can't be any worse than oxbow oat hay, which was literally HALF oats and pisses me off to no end (if you think I'm exaggerating about "half oats", I swear I'm not - I have pics to prove how bad it is!
).
another perk of buying from feed stores is that most will let you grab a little sample of each of their hays free of charge so your bunny can "taste-test" them before you commit to buying an entire bale.