fretman, You're welcome! The TB6600/THB6064 chip is rated for 50V absolute max. Most of the boards recommend 40-45V max supply voltage. Voltage can spike during decel (motors act as generators), so I would go with a 36V supply to be safe.
The current depends on what motors you use. The least cost supply is the switching type; the most reliable supply is the transformer type. For more reliability from a switching supply, I'd get a MeanWell brand rather than generic. For example, their 350W 36V, about $50 on Amazon or ebay, but I have not tested it yet.
Amazon.com: Mean Well NES-350-36 36V 350 Watt Ul Switching Power Supply 110-240 Volt: Electronics
Note with only 36V, the motors need to be low inductance to have reasonable torque at high rpm. I'd try to get 2.0 mH or less. I recently bought a 1.8 mH 400 oz-in from Stepperonline -- hope to test it soon.
Completely agreed that Gecko or Leadshine drives are fantastic, but for similar power they are 3x - 10x more $. For a cost-sensitive build, I know of no better option than the TB6600/THB6064.