If it is forcfully popping out of gear, it is because the dog teeth on your syncro ring are damaged to the point that they can no longer hold the gear. Basically, your syncro ring is foobar. While it is repairable, it is much cheaper to find a replacement transmission than to attempt to have the transmission repaired. There is no such thing as a transmission shop that is not crooked. They will try to screw you in any way they can to make a buck. I've been told this straight from a transmission specialist who has been in the business for 20+ years. Just buy a junkyard trans, swap it in, and learn how to shift so you don't break it again ;-)