I have always thought that Drives Warehouse in Dallas was OK, but slightly overpriced.
I used to buy them off the industrial section of eBay, but over the past couple years, even that part of eBay has become much like the rest of eBay -- i.e., overrun with either junk or companies that are selling greatly overpriced stuff. I guess that a good thing never lasts forever.
A couple thoughts -- if you have a 230 VAC motor, I would strongly recommend also getting a 240 VAC VFD. (If something looks like a typo here, I'll mention that motor nameplates usually state voltage a bit lower than the standard power company line voltages). While you might find a 230 VAC motor with windings that will allow 115 VAC configuration and also find a 120 VAC 1 HP VFD, it is very likely that the VFD will cost much more than a 240 VAC VFD with the same HP rating. The reason is that the switching devices (usually power CMOS transistors) for the higher current that it must handle at 120 VAC will cost much more than comparable lower current devices. There are also other cost considerations such s heat sinking and active cooling requirements. My gut feel is that 1 HP VFDs rated for 120 VAC operation are hard to come by.
Have you found a motor yet and do you know if it is specifically rated for VFD use. I know that a lot of turners have used ordinary three-phase motors and stated that there is no problem, but what they really mean is that they don't know that there is a problem because there was not a puff of smoke when they turned everything on. The failure mode is not obvious and does not happen suddenly so, depending on how it is used, a system may last for quite a while with a motor not designed for inverter duty, but performance does very slowly deteriorate which means that it may not be noticeable until performance gets really bad.