Interesting question....
* My Dad and I bought a new 60 acre bermuda grass hay farm about this time last year. We bought a slightly used JD 467 baler, a new JD 830 MoCo, and a new Rhino SWR-10 wheel rake. All together, we spent $50,000 on hay specific equiment. If you spread that over a 5000 bale life, you get $10 per bale in direct equipment costs (assuming you don't include the two tractors which we already had).
* Now keep in mind that last season was the hottest and dryest in Oklahoma in the last 50 years. So, the production that we got off the field was about a third of what I think it would do in a "normal" year. But the "variable cost" for us (which included fertilizer, diesel, and net wrap) was right at $30 per bale.
* So (not counting our time) I would say we had $40 per bale in the hay that we made last year. Given the dry year, we ended up keeping all of it ourselves and not selling any. But, I would say a 25% profit on top of the $40 cost would be the minimum that I would have considered selling the hay for.
Granted, last year was not a "typical" year (at least I hope not), but $50 per bale would have been my minimum had I had any of it for sale.