macbook pro 2011 bad keys how much to replace keyboard

I have a 15' MacBook Pro, late 2011, that after three years of minimal morning use (2 hours a day) developed trackpad problems. Took it into the Genius Bar and they were able to adjust a screw tension that resolved the issue. A month later I start having the erratic key issue that I've seen repeated complaints about in the forums. Letters E, R, T, I,O etc -- along that row -- type sometimes then not. The trouble seemed to start when I adjusted the keyboard brightness in the Keyboard function in System Preferences to remain on all the time (so there may be overheating, but the problem wasn't resolved by turning the function off altogether. Happens in multiple applications. I ran an Apple Hardware diagnostic and it said nothing was wrong. Tried some of the various fixes suggested in the forum (like pressing both Option or Control keys 5 times). Is a replacement keyboard really going to set me back $800? Given the amount of response from this forum about the issue, is Apple doing anything? And finally, if I do shell out the bucks to replace it (I may get an external keyboard for now, but that's not a good long-term fix), is there anything like keyboard covers or the like that can prevent such rapid deterioration of the underwiring?