Durable Weed Eater that can get job done?

I have a yard that is very unfriendly to any type of lawnmower and am in the market for a weed eater. I've cut my entire lawn with a weed eater before and I'd say it took me 30-40 minutes depending on how lazy i feel. I want a weed eater that will last and that will do it's job well, as it will be my only source for a manicured lawn. I have to cut the gr every week and a half or so. Any suggestions are welcome other than a goat? Thanks in advance.