I'm not sure of your needs, number of hives, type/size of entrances, etc. Or your desires, electric, propane, etc. But if you want an inexpensive propane powered evaporator for a few hives, it's really easy to build one out of brass fittings available in most hardware stores. Here's a description of a couple I've built:
This example used a threaded fitting that fit a vent hole in my hives. It could be modified by using a coupling with a piece of piece of copper pipe. It could flared and would work for a narrow bottom entrance.
DIY electric evaporators, using diesel engine glowplugs, are also easy and cheap to build. I links are here on Beesource.
Also, if you're using propane, don't buy the cheapest torch. Or this could happen:
And, if you're treating a few hives, at a time when you can open the hives and the bees can fly, it's just so much easier and safer to dribble oxalic. The treatments can be incorporated in your normal inspection routines. And for a few hives, it's just so much easier and safer than fuming them: