Like most things, they very quite a bit in quality. I'm assuming you want a converter/inverter to both charge the battery(s) and provide 120 volt power when not connected to shore power. As a rule of thumb, you probably want something that will provide more amperage than what you think you'll need.
Check out Camping World, one of the businesses owned by the sponsor of this forum. They may be able to provide you with specific recommendations and may have what you want.