Right Seat in a 135/121 Jet would require Commercial, Instrument, and Multiengine ratings. Figure $25-30K for that, assuming you went with a heavy-duty training schedule and did everything in the minimum required by FAR 141. To get HIRED right now you'd probably need 500 TT - some operators are not requiring minimum ME time, they just take you and throw you into class, with a predictably high washout rate.
Left seat in a 121/135 jet requires ATP, MEL, and type ratings. So add $15K for the type and the ATP checkride, plus whatever it will take for you to get the minimum flight experience to qualify for the ATP exam. Then plan on moving into the right seat for a while anyway, as no operator will hire someone as a captain unless they've already BEEN a captain somewhere else, or have been an SIC with enough time to upgrade to captain.
Left seat in a part 91 jet will require private, instrument, MEL, and type ratings. You could theoretically take away some cost for getting the commercial, but let's face it, if you're gonna build the time required to be insurable in a jet, you might as well get the commercial. So, figure $12K for the type rating in addition to the basic above, plus the cost of hiring a professional typed pilot to act as PIC while you gain the 100-200 hours your insurance company is going to want.
This was a good mental exercise, and it does a great job of illustrating why the traditional airline career path (excluding military time) is:
Phase I - the paying phase
Private
Comm/Inst/Multi
CFI/CFII/MEI
Phase II - the teaching phase. Here you build enough time and experience to qualify for an SIC position with an operator. Not much money, but at least it's a positive cash flow for flying. ATP may be obtained in this phase.
Phase IIIa -the professional flying for less than you made teaching phase. Here you fly in an RJ or turboprop for a small operator, getting practical experience, logging additional hours, and waiting to upgrade to captain.
Phase IIIb - Regional captain. You finally are in the left seat, responsible for the airplane and the passengers. Here you actually get to log the time the majors are interested in, jet time where you are acting as PIC.
Phase IVa - Major SIC - all your thousands of hours as a regional captain have qualified you to take a pay cut and move into the right seat of a major. Like phase IIIa, you're logging flight time, and waiting for a chance to upgrade.
Phase IVb - Major Captain - Now your pay depends on the equipment and routes you fly. You may get only a small raise if you go from SIC on international routes in 747s to Captain on domestic routes in a 737. Bouncing back and forth between Captain and SIC is not at all unusual, depending on airline health and your preferences.
If you go the 135 or corporate route, the progression is similar - you start in the right, move to the left, and there are quicker/slower paths depending on the equipment available, and salary varies with the size of the airplane and the role you play.
There's been a lot of hulabaloo over the relatively low times required to be an "Airline pilot" (regional SIC) nowadays. The fact is that most FOs accumulate time pretty quickly, up to the maximum 1000 per year, and the 200-hour wonder hired in January is ready for his ATP ride in another year and a half, and eligible for upgrade to captain too. There are some good rules in place about having one greybeard teamed with every rookie, and the safety statistics seem to indicate that it's working.