ap cost more because they r worth it they have more features than a router like the linksys ones theres four different ways you can run them.
1.access point, runs the same as a wireless router
2.access point client, enables you to use the ap as a wireless adapter, like a wireless card in your computer.
3. wireless repeater, no cord needed, uses an existing wireless signal and repeats it, as in another room in your house to get a better signal upstairs
4. wireless bridge, like you have a older non wireless capable desktop that is up stairs, you take two Ap (routers will not work in this mode) and you have one that on one end of a work place and the other ap is on the other side of the work place the two basically act as an invisible eithernet cord from one end to the other, (in this mode the ap do not allow wireless clients)
as for running a different firmware not doing it before and not knowing enough about it, i would screw it up and i dont feel like blowing another fifty bucks to get a new router.