they are not but Subaru GL's brats, Rx's and Xt's can be. you can pick up an Xt6 AWD for nothing, and it'll give a modern Subaru a run for it's money, it just does not have the horsepower, but that can be rectified.
there are some old honda's and toyotas that are great AWD rallycross cars. a BMW 325IX and these are just the AWD ones.
If you go 2wd, any old sentra or even a rusty cavilier can compete, and do well! keep the car small and light that is the real focus.