Firstly, its not really a good idea to venture into an eCommerce project without knowing PHP unless you are using a ready made store such as PowerStore.
Secondly, you need to request that your client provides you with the information in a format that you can import into mySQL using a tool such as Navicat or phpMyAdmin. Either that or charge them for the time it takes to add 10,000's manually.
The way that I see it, the client has two options. Either pay for your time for manual entry or provide the data in a workable format (i.e. one line per product) so that you can import it.
The key is to be up front and honest with your client. It will save you a lot of unnecessary pain in the long run.