I believe Iowa State University has a hay budget calculator on there website that you may find help full. Just some rough numbers for you though, assuming good quality used equipment. These are estimated prices of what I would want to use to do 50 ac. You could spend half of this and have what you need, but personally I wouldn't risk it for 50 ac myself.
Initial investment
80hp tractor - $10-20k
40hp tractor - $5-10k
Baler - $10k
Mower - $10k
Rake - $3k
Tedder - $3k
Thats $41-56K in equipment. That doesn't include anything to get it off the field. You either need several flat wagons, or an accumulator and grapple for your tractor, or a pick up wagon. Any of these option are probably going to add another $10-15k by the time it is all said and done. If your carefull and shop around I'm going to say you can get what you need, bare minimum of $50k.
As for establishing a field, most average around $400/ac, so add another $20k to your equiment for that. Now your at $70k min. to get ready to make hay.
That much hay in small squares you are going to need some help also. If you have an accumulator or pickup wagon, and a grapple on your tractor you may be able to get by yourself though, but doubtfull. Figure you may have 50 hrs per cutting, X3 for 150 hrs a year, maybe more, maybe less. You need to be able to pay yourself something, plus $10-20/hr for any hired hand. Then you also have fuel and maintance on your equipment.
On top of all of that you need to figure in either land rent, or your payments on the land, plus property tax, plus insurance, interest on your start up loan, or interst you losing by pulling it out from whereever it is. You also need to figure in your fertalizer cost ($100-150/ac/yr +/-) As you can see there are alot of number that need to be figured into this equation. That spreadsheet from ISU that I mentioned does all of this.
You also need to figure that all of your hay isn't going to be high quality horse or dairy hay. Chances are something will get rained on, cut late, or whatever else and your quality wont be there and will sell for less, if at all.
The ISU bugdet is on this page
http://http://www.extension.iastate.edu/agdm/crops/html/a1-20.html
Im not trying to scare you away from doing it, it's just a little more complex then some people make it out to be. IMO it's a lot to just jump into.