Have you ever considered an Access Database? With Access you can have an interface that your sales assistant would use and they could simply enter in the customers name or other information and find the customer quickly within seconds or less depending on size of database.
In years past I use to support Napa Tracs a software package that gave automotive garages the ability to track inventory, automobiles, warranties, customers, etc and this product worked very well. Many garages prior to this were trying to get by with excel spreadsheets and it was a big mess.
Depending on what your making quotes for you might find a software product out there that can avoid you from having to reinvent the wheel, although if you want a highly customized database Access is the way to go if you already have it as part of your MS Office package.