It's hard to say without seeing the computer exactly what's wrong but if you buy the used part on eBay you can install it yourself if you can turn a screwdriver and pay attention to detail.
You might just have a disconnected cable, or you might have corrosion due to liquid damage. You have to open it up and find out.
$80 in labor is RIDICULOUS, never pay someone that much in labor for something like this, it's total gouging.
You may have to replace the entire touchpad assembly, which is what surrounds the keyboard etc. I found one on eBay for $12 and free shipping, just search for "dell 1545 touchpad" and you will see it.
Take off the strip above the keyboard, then the keyboard itself. Disconnect the cables for the LCD housing, remove the LCD housing/lid assembly. Remove the touchpad/wrist rest assembly, put on the used one and reassemble in reverse.
Congratulations, you just repaired your laptop for $12 total.