How big? You can buy a dent puller or try a suction cup if it is a smooth even bent. PDR can fix smaller dents. Youtube has a video of how to use hot and cold to pop a dent back out. If its a repair that requires filler and it's large, your personal paint job will never look good. In that case, go to a shop. You can however do more than you think- youtube and online is your friend!

Depends on the damage, most will charge about 50 to 100 for poping out the dent. Add replacement fees if they have to replace the part

Depends on the size of the dent, whether or not the metal is kinked, and the location of the dent.

Depends