Autoupdating Assemblies

Hi group,

I have an estimating db that I have a table for items and one for assemblies and one for assemblyItems. The assemblies are like a header table where I have a title of the assembly and I add items from my items table into my assemblyItems table. This creates a actual cost for the assembly. So an example is this; (I am an electrical contractor)

Office with 2 Lights, 1 Switch and 3 Receptacles. $328.00 4 hours of labour.

This has the following items in the AssemblyItems table that will make up the cost of the assembly.

2 2x4 Troffers c/w lamps $68.00 2.4 hours of labour.

1 Box $4.00 .02 hours of labour

Wire, etc....

I would like it so if I update a price in my item list the linked item in my AssemblyItems table is updated and the assembly header is updated.

What do you think Is the best approach for auto updating, something that won't kill the speed of the db.

Thx,..

Jamie Lindemann