Is that the 75-300mm, the 70-300mm or the 300mm f/2.8? That last one would require a very strong head.

But since you wrote you don't want to spend too much, I assume it's not 300mm fixed.
I'm no expert on heads, still looking for one myself (combined with the Manfrotto 055XPROB).
804RC2 might be an option, or the
808RC4. They are expensive though. However, you'd best get good support for your camera, you don't want it to fall because the head is cheap and not made for DSLR camera's with longer lenses.
Click here to go to all Manfrotto's head that are reasonably affordable.
I'll now continue my own search for a good tripod head!
- Bjorn -