Here's what I use for about 20ac of hay:
New Holland 451 sickle bar mower.
If you are knowledgeable how to operate a sickle bar this mower is one of the best. I use it with either my
B3200 Kubota or Ford NAA, takes very little power to run and will mow 3-5ac per hour. I got a great deal on mine for $750 (needed a little work), but nice ones go for $1500-2500, new about $7500, and at that price you might as well get a small disc or drum mower. If you aren't mechanically inclined skip the sickle bar and look for a drum or disc mower.
G2 brand 2 rotor hay tedder, 3pt hitch.
Just a run of the mill Italian tedder, had a broken spindle so I got it for free. Took about $100 in parts to get it going. Works well behind either of my tractors. Probably $300-500 used for most.
New Holland #56 rollobar hay rake.
Needed gear box rebuilt, new tires wheels, and new tines along with some other part. Got it for free but had to put about $400 into it. This model is very old, somewhere between '59-67, the newer model is 256 and they sell for $1500-2500 used for a decent one.
New Holland 268 square baler.
Great little baler that doesn't require as big of tractor as the modern square balers. Got it from a friend for $1000, it's pretty old (mid-60's) but was used very very little probably less than 5000 bales. Paid $1000 for it. Stick with either John Deere or New Holland when it comes to square balers, they really had the best technology back then. On average I would budget $2500-3500 for a baler. I pull mine with my NAA (31.5 PTO hp) and it handles it well.
So overall I have about $2500 in my hay equipment including parts to get it going. If you paid going price for used equipment that was all field ready expect to pay as much as $10K.