The 18tz goes for around $179.99 new for the pullstart version if you shop around you should be able to get one a little cheaper. I have one in my RC10GT and it is a rocket. if you wanted to save a few buck you could go with something along the lines of the OS 18 CVR which runs around $129.99 I had one in an HPI firestorm and an HPI MT2. It doesn't have quite as much power but it is close and I found that it is a little easier to tune. If I was in the market for another small block engine I would probably give the LRP Z.18S Pro Spec 2 a try. I have owned this one yet but I have heard some very good reviews about this engine. power wise it falls somewhere in between the 18 TZ and the CVR but it is even cheaper at $119.99. Like I said I haven't owned one of these engine yet but I recently bought an LRP Z.28 Spec 3 for my savage and it is an awesome motor with ton of power and is very easy to tune. If that is any indication of how the LRP 18 should perform.

Another option for you is to check out the used market you can get great deals on any of these engines if you get them used. don't feel like you are limited to just size .18 engines either. there are lots of after market .12's that offer good smooth power bands with tons of top end revs which is really what gives you your high speeds anyway.

I also have a old nitro rustler with the 2.5 and I have found that it holds a tune pretty well but it is lacking in power. if you upgrade to anyu of the engine I have mentioned you will see a huge difference power wise.

Good luck with your choice!