Your cheapest option is to buy a nice used 60+ pto hp tractor for $5500 and a then get a real round baler.
Those micro round balers that fit your tractor are too expensive, and make a tiny round bale that is kinda awkward to handle - too big to manhandle, too small to use regular hay tools with and no savings on twine....
With the size of tractor you want to bale with you will end up with bales around 100-250lbs. The bales would probably look like and be the size of the ones that the early round balers made.
I have a 33 hp 26 pto hp mahindra. Last year i bought a 605 c vermeer round baler. I made over 75 5 foot round bales with it. No bs. It wasn't fast baling and i had to let her cool down often but i did it. It a difficult baler to use but fairly common. You can adjust the size of bale by tying anytime you want. I also hauled them off 2 at a time. One on the back spear and one up front. Could load a 3-4 foot high trailer no problem. The bales are just the right size to handle with a smaller tractor.A rear bale spear is nessacary though or else the tractors *** will lift when you try to move the bales..People thought my small tractor was a bad investment but my sheep ate well all winter at a lower fuel cost.