MFG S____y sells their Flexpruf 1" axles for $45 - $53, with various type ends. Their solid steel 1" axles are a little less. Running Flexpruf myself, but haven't had a good stress test.
I'll say this, it's my belief that you can put incredible torque on an axle like the 1" Flexpruf or solid, and it won't pretzel on you if you just have enough bearings along its length. That's why you can't ever open the bottom of a V8 engine and only see one bearing in the front and one in the rear.
Running 4 cast iron 1" pillow block bearings on my 15+ hp. right now, 4 instead of 3 mainly because ebay sells them in various lots of 1, 2, 4, 8, etc. Mine all came from Jeremywell and are 4K rpm's that are as good as any others. All have zerk fittings with caps, and elongated mounting holes in the castings.
I see you're thinking 50 - 60 hp., but the rule still applies. An axle can't pretzel unless there's enough room between the bearings to do so. Here's a tip: Use DOUBLE-SPLIT locking collars on everything, that just slap right on and get tightened without sliding anything off the axle ends to change/add parts. No harm in putting them on BOTH sides of everything on the axle, which strengthens the spaces between bearings even further.