D.B.
I did my screens myself with screen material (it comes in a roll like fabric) and accessories purchased at Lowe's or Home Depot. The staff there are very helpful. You could take one screen in and ask them. I'm not sure why this guy's estimate changed so much from $28 to $40 - are the frames particularly complicated or old? Also, a lot of places that do glass also repair screens - you could call around and get some estimates. Unless you are already committed to this guy and he picked up all your screens already. Good luck.