It also depends on how big it is and how much time it will take. If you think it's around an hour, and its really hard, I would ask for around 25, around half an hour 15-20. It all depends.
Mowing lawns, I had lawns that took 5 minutes that paid $15, I had lawns that took 20 minutes for $20. I had one that took 45(that was my record), but more like an hour for $30, and the best being my generous neighbor across the street giving me $60 to do the lawn that took 30-45 minutes.
Prices really differ. Just tell them a price, maybe a little bit higher, and say youre really not sure how much to charge. If they take the higher price, that's good, if they dont look good about it, drop it $5 to the price you had before and be like, I'll be nice and drop the price for you, and they will like it and give you business later.
dude, if i was abe lincoln in the 1860s, and a bunch of southern states decided to break off, id be like, dude, fucking take them, we dont care.-mnscratchskier