Mage, I've done my share of free lance type work on the side in a few job markets.
A few things to concider first -
Is it a job which will be supporting you or a hobby making a few extra bucks on the side?
Is there anyone else in your area offering the same type of service or goods?
How much of a market is there in your area for what you are offering?
What takes you 3 hours, can someone else do in 2 hours?
If there is a market and you don't have much competiton and it's just a
hobby, then concider making a "few" extra bucks a good starting point.
Everyone likes to charge $20.00 (or more) an hour for their time but
sometimes that just can't happen. You can always test the market with a
higher price, if no takers, lower the price. But set a minimum price
for yourself above and beyond your cost. Maybe add $5.00 an hour to the
cost of supplies and materials used as your minimum.
If you had other people offering such a service or items in your area,
you could get an idea what the market is used to and maybe start your
price just slightly lower to get your customer base started. Then as
business picks up and people like the quality of your work, slowly
start raising your prices.