I just got mine today, so I can't give you any user reports, but you'll want a Gimbal style head; cheapest you'll find is this one:
Bogen / Manfrotto | 393 Heavy Duty Gimbal Type Telephoto | 393
The
best Gimbal head is the Wimberly, which is close to $600 (just in case you thought the linked head wasn't "cheap").
As for tripods, "cheap" and "good" are generally mutually exclusive. Do yourself a favor and buy a
good tripod, because the cheap ones will end up being replaced a few times until you end up buying the expensive one you should have started with (and, ultimately, you'll have wasted a bunch of cash on junk). In particular when you have a jewel like the Pentax 135-600 F6.7, you don't want a cheap support setup dumping it on the ground!