I would buy some 12VDC box type fans or use CPU cooling fans that run on 12VDC, then I would add a small wall-wart type of power supply (the kind that has the transformer as part of the plug). The wall transformer will cost about $15. For safety, put a switch between the transformer and the fans.
You can buy 120VAC box fans. They usually cost a lot more, but the ones that I have are designed for continuous use. If you get that type of fan, you can just connect them through an On/Off switch directly to a wall plug without needing a transformer.