Great bag! I just recently sold two of my bags on Etsy and I too was a little nervous on what to price them at. One sold for $25 and the other for $30. I agree that $10 for labor is a good place to start. Take into consideration the type of fabric you used and other embelishments and don't sell yourself short. I did my first art/craft show and I sold two bags and received two custom orders. People will pay good money for a handmade item. If anything, start out by pricing your items a little lower and if they sell then gradually increase the price by just a little. I've done that and I've had good sucess. I'm not trying to gouge people but I want to be paid for my time and labor.
As far as making the bag more sturdy I have used fusiable interfacing on both the outer and lining fabric. It can make it a little tough to turn right side out but once you iron it it looks great. It's sturdy but it's not overkill if that makes sense. I'm still experimenting with different types of interfacing too.