I get mine from thewaxfactory on ebay - good service, and quality /value for money - approx £11-£12 per Kg for English yellow wax pellets.
A one pint tankard will absorb a little under 100g of wax. I've not tried the painting method (looks too much of a faff, unless you're only planning on making one or two tankards), dipping is quick and efficient, but you do need a good quantity of wax. As BR says, you're really looking at a pot to hold a couple of Kg of wax. A 16cm Zebra billy is a nice size and is just big enough to dip a tankard, and sits nicely in an old Prestige pressure cooker base as the double boiler.
Geoff