There is a price difference in 737 rating between airBaltic and Ryanair, but when you factor in the 70€ an hour deducted from your salary by airB for the first 300hrs line flying flown + the fact it will probably only be a Summer contract till end Oct, Ryanair doesn't sound so bad.
Agreed, for anyone with the rating, FR is not an option, as they cannot make money from you. Having said that I am not sure if airB will offer a F/O position (even the 300hr that you "pay" for) to someone who is not completing the rating there, as at the moment the 300hrs option is the carrot they can dangle to get someone to "buy" the rating with them. I think if you are already rated, you will not be hired by them in the current situation.
Motto, don't pay for a TR without a job offer, or at least the possibility to top it up with some line flying (even if I find the whole concept of this quite reprehensible, it must be said that the TR alone is REALLY a waste of money)