PCBs at home, dry film solder mask

I've been making PCBs at home for a while now, I went from toner transfer to UV film, and I'm liking the results so far.

Aside from the UV film, I've seen that there's also solder mask film, which you put on the board to make soldering SMD components easier and (I assume) to keep the copper from getting tarnished.

Except I've been searching on Ebay, and the only solder mask film I can find (Dynamask) is sold in Slovakia, and costs an arm and a leg compared to UV resist film.

I suppose there's something I'm not getting here. Is there a cheaper alternative to using solder mask film? Or a cheaper alternative that's made and sold in the americas?

It comes available now and then on eBay.
For home made PCBs, not really worth the effort IMO.
However, solder mask is just that, it keeps solder from adhering where it is not wanted during the soldering process.

For tarnishing use tin plating solutions by MG chemicals.
Liquid tin.

.

Soldermask is fairly essential for surface mount work to prevent the surface tension in liquid solder dragging
and tombstoning small components around. It reduces corrosion of copper traces in hostile atmospheres too,
but you can lacquer or coat the board after soldering with a conformal coating for more robust protection
too.