Help with new database table layout.

[Steve P.]

I'm hoping that someone can advise me on my table layout before I get in too
deep. I am a self taught Access novice so describing my layout doesn't come
easy so I have placed some screen shots at this link:
http://www.monkey-butler.net/msaccess.htm

This will be part of a system to control inventory at remote loctaions.
System must retain the use of existing barcodes which by pure luck are
unique but we will have control over issuing future barcode ID's.

There are multiple customers and some customers have multiple sites. The
same item may exist in multiple bins at one site. Pricing must be
admininistered at the Customer level from a linked file from the business
mainframe. The barcode must identify the item to the
Customer>CustomerSite>ItemBin level.
The layout shown seems to do what I want but a little voice keeps telling me
that there must be a better way.

Currently I have four tables...

tblCustItems - contains general item info
CustNum(PK)
PartNum(PK)
Desc1
Desc2
Weight
etc...

tblCustSites - contains info about the locations where the items reside
SiteID(PK)
CustNum
SiteName
Address
SalesRep
etc...

tblItemBins - contains inventory control info
BinBarCode(PK)
SiteID
PartNum
Minimum
Maximum
QtyOnhand
etc...

tblPrice - info comes from business mainframe in a linked table
CustNum
ProdNum
NetPrice
ContractNum
etc...

CustNum and ProdNum constitute the PK of tblPrice on the mainframe.

Thanks in advance for your help.
Steve P.