I'd rent a 800mm


http://www.lensrentals.com/rent/canon-800mm-f5.6-l-is/for-canon


a wimberley head:


http://www.lensrentals.com/rent/tripod-head-wimberley-type-ii


a mounting plate:


http://www.lensrentals.com/rent/arca-swiss-type-plate


and a heavy duty tripod:


http://www.lensrentals.com/rent/tripod-heavy-duty-carbon-fiber


roughly $460 for 7 days without shipping/insurance. Probably another $200 for that...