If you just want something that's ok in power, and relatively cheap, I found my HPI Nitro Star T-15 (generally around $65 on ebay) does a fairly good job. Out of the Nitro engines I own its reliable, starts in seconds, easiest to tune, and is just right for my truck. I estimate it gets my truck up around 30-35Mph. But I have my truck's suspension set high with masher 2k tires so if it goes too fast it will flip very quickly on turns. The glowplug that came with it, that was used in its break-in, I still use and its went through around 80% of a gallon of nitro and has yet to give me any kind of issues. Honestly after using the Nitro Star T-15 I'd recommend it to anyone just starting nitro as a good beginner engine.

BTW I also got a G3.0 but I perfer the T-15 over it personally. I don't really need the increased power and speed the G3 gives where I drive. I mainly keep it as a backup in case my nitro star ever goes out on me