Skip,
That is true, there are some options if you can't afford the price of an electric screen. You might consider a fixed screen, if that is not practical you might look into making a manual roll-down screen yourself. A pull-down screen is probably not a very good idea if you regularly raise and lower the screen, because it does stress the screen material and may cause warping or other changes over the life of the screen. Also, the spring mechanism of the pull-down screen is probably not as mechanically reliable as an electric screen.
Anyways, if you are inclined to make your own solution you could probably get the screen on a roller (and maybe even in a case) and rig up a simple chain or rope to roll the screen up and down, this would prevent any stress on the screen material and it would probably be pretty affordable.
Regards,
Kam Fung