it might not be your disc--it could just be your rotors or your pads were put on wrong again.
hopefully your disc isn't warped--thats a good bit of $$.
take it to any autoshop and many tire shops also specialize in this as well and get some opinions.
my guess would be your rotors (discs are pretty hard to warp unless you've been in an accident). you can do these yourself or you can get an autoshop to do it.
rotors + pads + install is about $150-$200 at a typical autoshop. do it yourself and obviously all you need is $$ for parts (about $70-$100)
i just changed the pads
then get the shop to take them off & install on your new rotors (if this is the problem as i suggested).
anyway, pads aren't very expensive...very likely you will pay the same whether you get new pads or not because the cost of taking your 'new' pads off your 'old' rotors and installing them on 'new rotors' probably will be the same as just buying 'newer' pads on your 'new rotors'...unless you do it yourself, of course