Well, to be honest, I'm thinking you've done everything possible within your budget.
Now, moving along, if you're looking for extra speed (eg pulling away) or generally accelerating through the gears in a nippy manner - we are talking hills.
Prefereably, going down them.
Remember, gravity is free
Oh, and try disconnecting your brakes. Not completely, now that would be dangerous, but make them less effective. This will change your driving habits very slightly, in making you not wanting to stop. This in turn, will make you drive faster.
Helpful tips, on a budget.
Tin