My Little Giant 50 came out of a barn way up here in the highlands, for $500 and in need of nearly a complete rebuild. I have less than $300 and six months into the rebuild and it runs great. Luckily the clutch babbit did not need to be replaced, although the main bearings had to be poured.
They are out there. Networking to the extent possible will help. Finding out who does or used to do ironwork within 100 miles of you may yield results.
Go to the power hammers page at anvilfire.com. You can learn a lot there- there are design plans for building hammers, as well as many pics of "junkyard hammers" built out of whatever by smiths.
If you live near a significant junkyard, one with auto parts and old machinery, and if you also have at least a 230 amp stick welder, drill press, chopsaw and a few other things, you could probably build one for cheap.