The high price variability has to do with the multiple ways a HDD can fail. Also, how badly the disk directory(MBR), or volume table of contents(VTOC - IBM) is messed up. If you have had the worst happen, you've had HDI, or head to disk interference. In this case, you will be lucky to get 5-15% of the data back, mainly because the detritus of the head and armature have scatter across the platters abusing all the tracks along the way.
If the arm is stuck to the landing zone rest(this is a common failure on drives from a certain vendor), you have a very good chance of full recovery. Of course, if it's a problem with the drive motor, or the armature coil, that's not a bad fix either, and should get plenty of data back.
If you've heard any kind of clicking or ticking in the past, it's pretty sure a head to disk interference(head crash) and recovery unless you are on a forensic mission usually isn't worth it. No matter who you choose to do the work, have them check for head crash first, and if it's positive for that, ask a lot of questions about cost, and probability of recovery before turning them loose on a wild goose chase.