There are so many different kinds, yet they all look the same and are priced differently

I am considering using one with either a 46 two stroke or a larger one with a st 90
Which ARF is the way to go. What is the best bang for your buck.

I also am doing this chem project at school and my idea would involve using a nitro engines. What a perfect excuse to get a new engine. So, what would be the cheapest 46-53 that would fly a 40 size profile. I was looking at the TT 46. Any cheaper engines in the same department. I fly all OS at the moment but the budget for this new plane is 400 out the door.