When you say "larger" how many clutches are you looking to have at one time?

The Nature Spirits are awesome but very expensive ($500 + with thermostat) and not what I would consider "large" 4-5 clutches depending on how you set up the egg tubs.

Personally I would build one. The coke/pepsi fridge conversions are awesome (assuming you can find one - as they can get expensive too)

Here is one I built - cost me $50 in materials ($150 for the flex and thermostat) - and it will hold 15+ egg tubs.