How much would it cost to replace for 4 molars on my lower jaw (2 on each side)?

I'm a 21yr female and all 4 of my lower jaw molars (2 on each side) are in really bad. I've already had one taken out last summer, so I'm now left with 3. I understand that if I don't do anything to replace them asap, I'll suffer boneless and other complications. If I have the remaining 3 extracted, what kind of replacements would you recommend and what would be the average cost? Long term, I'm hoping to get dental implants so I would love to know the average cost for 4 molar implants as well.