cheap duck fat?!?
Define "cheap"! The least expensive place I've found is Nicole's in South Pasadena - I paid $14 for a one-pound container, about a liter size, which was almost exactly half of Monsieur Marcel's price (and the same brand, too!). As for rendering, stovetop (or hotplate) works just fine. All you need is a reasonably heavyweight pan, and start cooking your chopped-up raw duck fat in some water at a gentle simmer until the water's all evaporated (no more sizzling) and the fat is clear, then you strain it.
Here's a tip- If you have a good relationship with a small food business owner, they might be willing to help you. Keep in mind- you should have an existing relationship before you bust in and ask them to start carrying duck fat (or other items not usually carried) for you.
That said, I used to get rendered duck fat for my customers- a 16 oz container ran about $13 retail, a smoking deal. I did NOT carry duck fat on a regular basis- this was a special order thing. But, since I had to buy by the case, I would have to get a list of people together before ordering. I think it's probably available to retailers just about everywhere, they choose not to carry it because of storage, etc. Don't insist the business get it for you, help them by putting some guaranteed buyers in place, and I'll bet you can get a better deal that WF.