I have a ballhead: Markins Q-Ball Q20 with Lever Release which I use for my Nikon D90. I just bought a HF G10 Canon camcorder and would like to mount it on the Markins. What is a cheap and good bracket that I can buy for my hf g10 that will help me operate it with the q-ball?
Cheap and good rarely go together but you have bought into one of the most expensive release systems on the market. That's OK since it gives a firm grip with little play, except that it will be hard to find something genuine and cheap.
What you are looking for is a universal camera plate with a list price of $55 USD. You may find cheap knock-offs on eBay and they will be just that. Mind you, this is not a sophisticated device, so if it is not perfect it may be too loose but it won't damage the rest of your gear unless you do not notice and something drops, so test first if you buy a fake.
I agree with you that plates are much more expensive than they could be, but I also agree with Itai's response that it's just an expense that's best to get over with. On the plus side, if you get a universal plate, you'll have something that should last a lifetime and will be usable with future equipment. One universal plate that I like is the Arcatech universal that's fitted with a cork top. The cork let's me tighten the clap to a point where it won't easily slip without feeling like I'm going to crush a plastic-bodied camera. While it's not cheap, it's quite reasonable compared to some other options.