buy only neccessary players (buying say 4-8 players at once does mess up squad harmony) spend say 15 million on a good RB as you say you need, maybe another good player off the transfer list that you need decent cover for in your team i.e. Gk for eg.
then take some of that money (transfer) and put a substantial amount into your wage budget and make sure that you are easily +25 000 a week in the postitive! this will mean that the cash is still in the club and if not used, will get put back into the club, this helped me alot, i was in a similar postion as you, had no transfer cash for 3 to 4 seasons then got my 33 million budget (after alot of hard work) and spent about half and reinvested back into the club
hope this helps