i paid $200 but most of that is just the parts. the labor is cheap like $30 or something. it's not like you are saving a ton of money doing it yourself. in my experience a good trimmer never has any issues. i have a honda trimmer that's 15 years old still on original spark plug and works perfectly. i changed the fuel lines, primer bulb, and got a new air filter after 12 years. it's never needed to be "worked on"
the trimmers that need to be worked on are usually better off being thrown in the trash. once they are worked on they never run right again and don't last long after being worked on. honestly there is no reason to ever need to change out a carb unless you leave gas sitting in there all winter without fuel stabilizer in it. all 2 stroke oils have stabilizer in them so you should never have any problems with a carb.
i dropped one of mine and that's what tore up the carb but apparently it tore up a lot more than that as the trimmer was never the same and didn't last very long after the repair. i should have just tossed it in the trash and started over with a new one. it was a 4 stroke husqvarna with the honda engine. that one only lasted about 3-4 years. it's funny because it has the same engine as the 15 year old one i have that has been perfect. i guess the drop killed it that's all i can figure. if you want a trimmer to last don't drop it or let it fall off of something and land on the carb.