when I bought my 500mm f4, I went through the same thing... Man I just spent $6200 on a lens... now I got to spend another $1000 for legs and gimbal head...... but let me tell you... just do it... and do it right the first time...
I have the benro gh2 gimbal and benro c-397ms legs... bought them from dc stuff on ebay and they are great..... good combo...

. At least I can tell the wife I have to get it. 
