I remember somewhere it said 5000 credits times contribution rank or at least I thought it did. But I can't find that so I have no idea where I got this number? does it say somewhere what value the item can be?

I couldn't find that either. Considering that AoR page 50 mentions them being able to choose a vehicle or starship based on Rarity (not on credits), players might exceed that 5000 per contribution rank easily. A 80.000 credits Y-Wing is only Rarity 4, and as such can be chosen at Contribution Rank 1.

The same goes for a piece of equipment. Page 50 lists the options as Rarity 3 plus Contribution Rank (so Rarity 4 at Rank 1). It does not mention specifics about the amount of credits, ust the Rarity.

Also, AoR pages 325 and 326 don't add a set value (per Ranks or not).

Of course, all is at the GM's discretion. And this Contribution reward comes on top of the group starting resources, such as a Y-Wing squadron or a Lambda Shuttle.

In theory, there is no credit limit. If you start getting a high enough contribution rank, you might be "gifted" with the headache of commanding a cruiser or a major base!