RJ type
I agree with the others. It's not really worth it to buy what is really an esoteric type rating. I say esoteric because the training is not commonly available to the pilot public at large and really available only to operators. You've already discovered that.
Your best chance at getting "the interview" is to offer essentially the same credentials as others offer, i.e., in a nutshell, plenty of multi PIC. You can get that as an MEI. If you can land a job flying in scheduled ops, i.e., multi freight or checks or something like that, so much the better. If you show an RJ type on your resume, it may be a negative because it could type you (sorry) as an oddball. Commuter recruiters expect a particular profile in their applicants and don't expect them to have type ratings. Something odd or different about an applicant without apparent explanation raises red flags and invites the round file (which is one reason why I regard recruiters as coneheads - they have this narrow point of view). The exception would be applicants who have types but also legitimate PIC experience in their aircraft.
A commuter might send you to an RJ immediately if it has the need. These days, though, it probably will not, so you will be assigned to the best aircraft your seniority can hold, which may be a 1900 or a Dash. It may be a few years before you can bid an RJ. By that time, you will have forgotten more than what you learned in your RJ ground school. Moreover, they want to train you their way and what you learned before might interfere with how they want to train you. That could hurt you.
In my day, many people, including myself, bought Citation type ratings. I did it because I thought it would give me an advantage if I could show I could pass a turbojet training program. Also, in those days, American Eagle was giving sim rides in a Citation sim. Well, several months after I took my type, I got an AE interview and was put in the sim. My type helped me not one iota. The sim flew completely different than the airplane. I do believe the type helped me land a couple of senior instructing jobs, but did me no good for getting commuter interviews.
Good luck with your plans.
PS-to the General: I went to five interviews or screenings eleven-twelve years ago. Nothing has changed. Take it from me, the interviewer controls the interview, not you. Don't be a wise guy; answers that you propose will accelerate your trip home. I remember my very first interview at WestAir in 1990. The Chief Pilot asked me to describe the emergency extension procedure on the Seminole. In other words, even if you have zillions of time in a 172 from several years ago, be prepared to answer questions on it.
PPS-Great suggestion below about getting a glider rating. I knew someone who got a job with Express I in Memphis or Nashville, I can't remember which, in part because of his glider rating. His interviewer was also a glider pilot, they bonded, and the rest is history.