Reg the budget check in Shopping cart

Hi SRM Gurus,

We are having a requirement that while creating a shopping cart system should check for the difference of budget amount in R/3 & open shopping carts in SRM and should allow to create SC only if the SC amount less than the difference. Can you people pls suggest the best way to proceed.. Is there any BAdI exists...

Thanks in Advance,

Chandra Sekhar.