It is not difficult to replace yourself. You can pick great condition top cases up on eBay for under $40 shipped.
I would get a Penryn/Santa Rosa Top Case rather than an older style as it has the current keyboard layout for the function keys to be more useful in Leopard/Snow Leopard.
The possible part numbers are 922-8264, 922-8265, 661-5075, and 661-5076. Be sure to tick the "Include title and description" box on your eBay search. Read the item description carefully to make sure you are buying a top case in excellent condition as all will be used. The same holds for parts web sites that are charging $150+ for the exact same thing.
922-8264 - 2006/2007 MB White (some Santa Rosa's/Penryn top cases show up here)
922-8265 - 2006/2007 MB Black
661-5075 - Santa Rosa/Penryn White
661-5076 - Santa Rosa/Penryn Black