Dokan is free and open-source:

http://dokan-dev.net/en/

There is an SSHFS module, but make sure you download the small zip containing updated binaries if you use the .5x Dokan library (which you will I'm sure).

I'm using it now and it works perfectly (a bit slowly, but whatever). It doesn't have any sort of logic built in to reconnect automatically or anything, but the price is just right for us cheapo's who like our source's open.