Customer's own prices and shopper group discount

[stAn99]

Hello, i would like to ask about your opinion or suggestions on what would be the most effective way to set up a shop with this specifications without core modifications.

The shop uses multivariants where all data are imported from 3rd party remote MS SQL database, so no VM backend is used and it's up to me to import it the most effecient way possible.

The problem - the product price requirement is to:
- some customers will have their own "listing prices per some products"
- for every other product there should be a generic discount applied (retail minus 10% for example)
- VAT will be charged fromt he discounted price per VAT status of the customer

my idea is to:
- use new shopper group per each customer with own prices + associate those prices with the shopper grop
- the question is what is the best way to associate "fall back" discount for products which don't have custom prices

inaccepted solution is to import all retail prices per customer since this would mean 1000 customers times 20 000 products would have a singnificant impact on the database where data would be repeated.

thanks, best regards, stan