A rocket grill, you say? I'm intrigued.
Turns out, a rocket grill is "super mega" way of describing an crazy efficient charcoal grill, which uses a tiny amount of fuel to create searingly high temperatures that mimic commercial wood burning fires, upwards of 800°F, perfect for pizza, steaks, and shellfish. Instructable-r dlewisa came up with a super inexpensive way to make one at home, using easy to find and expensive pieces you can find at any discount or hardware store - a Weber Li'l Smokey Grill and a standard chimney starter. Since lots of stores are likely closing these products out to make room for fall and holiday gear (?!), you can probably find these on megasale right now. Or, my local Craigslist has several instances of both pieces at under $15 each. Even at full-price, you're only looking at $40 or so.
The idea is to cut the bottom from the grill to allow the chimney to sit directly above it, capitalizing on the glowing hot heat that happens in a chimney starter with a single sheet of newspaper and natural chunk charcoal. The legs are removed from the grill and added to the side of the chimney starter for stability. The author was able to have a friend weld his together, but with careful cutting, it's not necessary, plus, you'd be able to disassemble it for easy storage.
Get the full how-to at Instructables: Super Mega Charcoal Grill (Rocket Grill)