How to get all product in minimum value from different vendors??

[amit]

I have 100 items and 10 vendors.
Vendors bid on that items like

Vendor1 Bid
Item quantity price Total Min-require
Item1 10 10 100 200
Item2 15 20 300
Item3 17 17 269
---------------------------------
Item100 10 10 100

Vendor2 Bid
Item quantity price Total Min-require
Item1 10 12 120 200
Item2 15 16 240
Item3 17 16 272
-----------------------------------
Item100 10 10 100

Vendor3 Bid
Item quantity price Total Min-require
Item1 10 11 110 100
Item2 15 18 270
Item3 17 17 289
-----------------------------------
Item100 10 10 100

I want to find solution with low cost and optimum value.
You are free to buy like buy 10 items from vendor1, 30 items vendor2
like this but satisfy min-requirement of that particular vendor .
But you get the minimum cost and display it.

Also 1 main thing is suppose I am taking item1 from vendor1 - 100
rupee but it not satisfy min-requirement of vendor1 i.e. 200 > 100.

I can buy item1 from vendor3 bcoz price =100 and satisfy min-
requirement of vendor3

But I can buy item1 and item100 bcoz item1+item100=200 and satisfy
min- requirement of vendor1 and lower cost than other vendors.

How to do this??
which algorithm to use greedy or Knapsack or any other cost
optimization algorithm...

How to get items in minimum cost??