Bandwidth Question


I am working on a multi-channel sales project for a client using web services. There will be a requirement to run some kind of shell script every 10 mins or so to check for sales and if need be, add or remove listings on several ebay accounts.

They have about 1000 products, 3 ebay accounts and 2 websites and I am struggling to calculate a figure for the additional bandwidth requirements for hosting due to these web services transactions.

I wandered if anyone might be kind enough to supply some ball park figures based on their own experiences and stats.

Many thanks in advance.