For laser only, check out the Lasermax guide rods on sale here for $170-300
. Their price is great on the XDtac models (5"), but for other models you might be able to find a better deal if you shop around.
They're reliable, accurate, and best of all change nothing about the feel of your gun. Unless you want a tac-light as well, it's best to avoid anything rail-mounted in my opinion.