Wattage for arcade PSU?

[Vertigo]

Lo chaps,

Quick and easy one this.
I'm in the planning stage of building another Super Gun and want to know what's the recommended wattage for a PSU to supply it.
I don't want something super juicy on the lines of an XBox and it won't be powering anything excessive like a Model 2 board or anything like that, but it has to be able to withstand enough draw to power something fairly current heavy like a mother/daughter combo e.g. CPS2 board with its fan or an MVS system.
Reason I'm asking is that I don't want to use more electricity than I really need to and I don't want it to generate too much heat as the PSU will preferable be enclosed within the main unit and without a fan.
Any advice appreciated.

Cheers.