I'm assuming you didn't purchase AppleCare before your original warranty expired?
The multiple keys not responding certainly sounds like a failed keyboard but you typically see stripes of keys fail. For instance, the last failure I saw was the F8, 9, O, L & > keys stopped responding.
You might try to boot to your recovery disk (holding command + R while powering on) to see if the keys respond there. If all seems normal while booted to the recovery disk then you're likely dealing with a software issue of some sort.
Alternately, if you don't have a firmware/EFI password set, you can try to reset the PRAM. This will accomplish two things, if it's able to reset the PRAM then it's a lot less likely to be a hardware issue & the act of doing this might just clear up the problem. Alternately, if the reset isn't accomplished then it's a lot more likely to be a hardware problem. You can reset the PRAM by powering on your Mac while holding "command + option + P +R", continuing to hold those keys until you've heard it chime twice. If it never chimes twice and instead boots then it's not able to reset the PRAM, pointing to a hardware problem.
Assuming it is a hardware problem you would need to replace the top case, typically a $250~ repair ($150~ for the part, $100 labor) through most AASPs.