Where can I get a cheap Ghostbusters Proton Pack?

Okay, so I'm not gunna be picky, Halloween is almost here and I need a Proton pack. I dont care if its the inflatable one or a custom built one, I just need a cheap one. I had the inflatable one but my son busted it last minute, so if you have that one and are looking to get rid of it help me out! Not looking to build one, as I dont have many supplies in my house to do so. Bustin' makes me feel good!!