Ah, ok. Well, you have a few options. You can do what's called a "Mini-Me". This is where you just swap the cylinder head for one from an EX Civic. This will give you VTEC and a few extra horsepower. Or, you could just swap the motor out for an EX motor. It will bolt right in and give you similar gains to the head swap. EX motors (the D16Z6) really aren't that expensive, so for reliability's sake, it might be best to just swap the whole motor.
If you want to go B-series than you have two options for the price range you listed. You could either do a B16, or a B18B (LS swap). Either one of those would be a nice upgrade for your chassis.
Keep in mind though, if you're having a shop install the engine rather than doing it yourself, than you're probably going to need to budget another $1,000 or so. You're also going to need to budget more money for the auto-to-manual swap, probably another grand for that as well (for labor and parts).
If you're limited to $2,500 like you said, then you might want to look into the Mini-Me or D16Z6 as opposed to a B-series.