When I was in high school I was doing a lot of yards, including 1 local cemetery that required almost all weed eating because it was OLD (and huge). Anyways, I saved up and bought a Stihl for $400. That was 1995, and it still looks and runs brand new today... which reminds me, I need to go and weed eat the fence before I leave for Alabama.
Buy something that is going to last... my dad just bought a new Echo. I don't think he likes it as much as my Stihl because he wants to trade with me.
Pay for something that will last, and another piece of advice - buy whatever you get from an actual dealer. Lowe's and Home Depot don't carry the same grade of equipment that the dealers sell... and it does make a difference