some people charge by the size- like by the square foot. it is hard to estimate an hourly rate- unless it's a pattern you have done before & know how long it takes you- a price should be agreed on before you cut a single fabric.
maybe do a little (window shopping) and even call around-visit websites that offer this type of thing & see what it costs to purchase- or have someone else make---then adjust to reflect what seems fair to you. or you can figure out the yardage amount of fabrics used (even though you are cutting up clothing- you can measure a block- multiply the size into yardage requirements if you were purchasing- figure in backing & batting (as in 24" x 100" = 1.66 yds- so figure 1 3/4 yds- x 2 for top & back= 3 1/2 yds- add batting- then multiply by 3---so, if you pay $10 a yard for fabric you would need $35 for fabric, add (a guess $10 for batting) so $45 x 3= $135----does that seem fair to you? or you can add a bit more- or subtract a bit---oops- i forgot to add in binding too---some add in thread too---
you can come up with a formula like this to have a base to start at if you plan on doing this kind of thing for people..