I Joined two pieces of copper sheet using Stay-Silv 5 solder, Stay-Silv flux, and a MAPP torch. Cheap supplies, cheap tools, not a complex process. The solder and flux can be bought at any welding supply.
The solder melts at about 1600 degrees and is one of the hottest ranges I have worked with. Even so I find it easier to work with than other silver-solders with lower melting points and much easier than working with soft solder. The Stay-Silv 5 in particular is very good at bridging gaps and filling recesses.