In the Mercenary Books there is a way to look at using a formula to determine Supply Units (SU). From there the Referee can say that 1 SU can equal 100 credits, but this negotiable. (pg 32 Book 1). Mercenary Book 2 gives an idea for a squad costing "Credits: Cr10000" for the Travellers just to outfit (pg 7 Book 2). The books also give some Mercenary Companies and examples of how much they cost. There are scenarios that also give some ideas about cost.
The main question, as we all know, will the players and the Referee have fun with determining the credits or is it safe to say, "You are in debt and need this payday..."? What your group determines as fun and immersive will vary.