I'd be surprised if you couldn't do it for under $1000 without trying hard.
Like I was saying before, water cylinder heating elements I'd imagine would be good and I think mine at least is 2kw. You can get a marine tank heat controller for $200ish, 3-4 of those water cylinder elements at $100ish(I think) each that's $600 for 8kw of heating. A bit of plumbing, wiring and relays for a few hundred more. Right around $1000. And, I'm sure there are better/cheaper ways to do it, but this would all be using pieces I think could be easily found.