Solder "Slugs" or pellets are not cheap either (£27 from amazon), I guess you could make your own by melting a load of solder into a small pot.
Yes, but it takes very little. I wad up non-resin solder, and melt it in a cup made of tin foil. VERY cheap. And it takes very little. A small slug (1" diameter) will last a few months if you build alot.
Cheers,
Will