You don't need to buy, and especially new.

Go to the local small engine repair shop and ask if they have any old engines you can have.

The first time I did this I got 10 Echos. and all but 3 had good piston and cylinders.

Look for SRM-2300, 2400 and 2600 series string trimmers. The 2100 series is okay, but small.

Hedge trimmers are a 2 ring engine.

Homelite: Look for the 33cc chainsaw. Easy to convert plus it weighs the same as the smaller engines.
The one with the black airfilter cover are suppose to be the best ones as far as performance.

You can build a conversion engine for less than $100.00
And it will run as good as a new engine off the self.