Are you looking for a stick edger (like a weed eater with edging blade) or regular 4 wheeled edger? For a wheeled edger a good used McClain would be my choice. Ive used them since i was a kid. I see the pros mostly using Stihl 4-mix 90's for stick edgers. Also a weedeater with the green Stihl X line works well if your careful.
You can find good used McClains for well under $100 around metro Atlanta. Many that just need a carb cleaning are sold for $50 or less. I paid $35 for my Honda powered one at a yard sale. Of course the blade was worn about down to about 5".
I have a older McLane Mowers brand edger with a little Briggs engine. I prefer using it to the stick edger I have for my Stihl combi. It is less tiring to push around keep going where I want compared to the stick edger.