Copying several worksheets data to a master worksheet

[hairy]

I'm a newby to macros and would appreciate any help to achieve the following
I may be going about this completly the wrong way, but here is what I want to achieve.
I've got several worksheets that are used for storing different suppliers products and prices.
These worksheets are used to input any new products & price changes from suppliers, usually done by copying and pasting the entire data in the
appropriate worksheet with the new list from the supplier.
Worksheets are named ACM ACA Avon Crawford Graphis Larson Visual
Only 2 columns A & B are being used, A being "Product" & B "Price".
Another worksheet is called "Master"
that has the combined data from all the other worksheets.
I use "Master" to search & maintain quantities and total stock prices etc.
I would like a macro that would copy only new Product entries or changed prices from all my Suppliers worksheets to my Master worksheet,
so it has to check to see if my "Master" worksheet already has the product entry first
if not then add this new row at this position
if exists already then check if the price has changed
if changed then replace price

Again any thoughts appreciated