Pricing lookup tool from table of data

I have been trying to create a slick look up tool for vehicle servicing prices that calls on data in a table.

The end user will select the make of the vehicle (Fiat in this case) then the model, fuel type, engine size and so on.

Finally, at the end, they will be presented with the price of each service on that vehicle for the next X services.

It kind of works as it is but I would like the data validation boxes to be dynamic as currently you can select a engine derivative that is not fitted to a model of car and it will return blanks.

My concern is that the end users will have to search through a few blanks before they get one that works and so I wish to avoid this by dynamic menuing.

I made it sort of work by a few different ways but have then hit a wall as it needs to consider several bits of previous date (Make, Model, Fuel, Engine size etc) and I can only make it consider one previous piece of data.

Any ideas or assistance gratefully received.