I think there might be a minor error with bulk pricing + rain check, or else I am not understanding it properly.
I set up a situation where I had two bulk pricing (giving 2.5 multi) + rain check, effectively having the raincheck give me 2x the total value. However, my assumption is that this would also effectively quadruple the amount taken from the budget. Instead it was consistently reducing my budget by $20. I then tried the next level with a single bulk pricing and rain check, and again it reduced my budget by $20.
It didn't really matter, as by the time you have assembled the combo the values presented are likely to be able to cover the cost, but it did confuse me.