Its difficult isnt it, having purchased the canon 600mm and a new tripod, you start to think, my god I have to stop spending this sort of money on a hobby,
I hear the manfrotto one is cheaper and quite good, guess the answer is to look around for a second hand one
The Gitzo 3540L is a superb tripod and with a max load capacity of around 40lbs it's more than enough tripod to support your 600mm f/4L.
I currently have three tripods, one being a Gitzo 3530 LSV which I use with my 500mm f/4L and it's easily the best tripod I've ever owned. It's superbly strong, but light enough to carry, and the non -stick twist locks make it a breeze to quickly erect and take down.
I can understand you feeling your wallet is taking a battering, but there's no point in forking out for a lens like the 600L and skimping on the tripod.
You'll know you're carrying that 600mm around - the last thing you want is a heavy tripod adding to the burden and not necessarily being pleasant to use or really up to the job.
You're not going to get a better tripod than this especially at this price - I'd seriously urge you to snap it up while you still can.