I am paying $60 a bale for about 900lb bales of orchard grass here in southern MD. I have seen round bales as high as $365 per ton, though. Round bale prices can also fluctuate because you can have bales that are >1200lbs and you can have little bitty 6-700lb bales. You should expect to pay more for bigger bales, less for smaller bales. Good bales can be more expensive, but not always. But crappy bales should always be cheap.
If you can get your seller to show you a weight ticket to prove what his bales should average, that is awesome. You shouldn't be tricked into paying a 1200lb bale price for a bale that weighs 800lbs. The dimensions of the bale often determine it's weight, but not always. So if you call on some hay, ask them the dimensions, AND ask what baler they use. Certain balers make certain size bales, and some sellers will lie about their bale size, and the truth comes out when you ask what baler they use. Those are the people you don't want to buy from...
While it is true that you can often find yucky, moldy, good-for-nothing round bales, that is not a blanket policy. It is also a misconception that ALL round bales are "cattle hay". The fact is that round bales are preferred for large cattle operations just for their ease of use. It is a heck of a lot easier to move, store and feed a 1200lb bale vs. 24 50-lb small square bales. Especially when you have to feed 4 or 5 TONS of hay per day! So, yes, you will generally always see round bales fed to large cattle operations.
But round bales are a perfectly acceptable and nutritious form of hay for horses. You just don't always see them fed because the average backyard horse owner does not have the equipment to move, store and feed them. That is why most horse owners prefer small square bales, because you don't have to have anything special to handle them. Just strong muscles and a good back.
People that bale hay for a living, for their income, put as much care and attention into their round bales as they do their small squares. They are cut at the same maturity, and baled at the correct level of dryness. ANY hay, whatever bale form it is in, runs the chance of being moldy if it is baled too wet, or is stored wet, or without proper air circulation. There are people out there, though, that do not care about the quality of their bales for whatever reason. Those are the ones you need to watch out for. Does the guy selling you the hay have honesty and character or is he a used car salesman???
You can't always judge a round bale by the outside. Bales that are stored outside, which is a perfectly acceptable form of storage in most climates, will look and smell and be moldy on the outer layer. Peel that layer off, though, and inside is bright beautiful wonderful hay. I've fed round bales that have been outside for 2 years that are beautiful inside, without any mold. Yes, they do lose a small percentage of their nutritional value as they age, but that isn't a big factor for my herd.
Hay testing is great, but nutritional value can vary from field to field, and cutting to cutting. So just because it is tested doesn't mean it is always consistent results. You'll often need to expect to pay more for hay that is being sold as tested, so you have to determine what value testing holds to you.