does the description of the material change over time?
if not then pull the description as required in a query using a JOIN
at first glance you could convince yourself that the cost could also be brought across as required, but Im guessing cost will change over time, so you need some form of storage for the cost at that point in time.
whether you do that as a column in materials sheet usage or model some cost based on time as a sub table in tbl materials is up to you
what you could do is when using the form is to stuff the material cost into the combo as a hidden column, which coiuld be a neater way of doing it.
OR just use dlookup to retrieve the cost in the combo's afterupdate event
certainly that will be easier than using a hidden column inside a combo.
incidentally you need to think carefully about your naming
don't use reserved words, it can and probably will bite you int he backside at some stage.
avoid using spaces in column/table names. if you want soemthign thats pretty on the eye set the columns caption property at design time. be consisten use either all lowercase_separated_by_underscore Or CamelCase
use abbreviatiosn where appropriate but retian the legibility
how likely is sales tax to change over time. if it does and you need to monitor that then you need to define the sales tax applicable at a specific point in time, or time period. eg sales tax 1.25% from 01 Jan 2013 to 31 Aug 2014
1.5% from 01 Sept 2014 on
your design will beneift from understanding normalisation
in a properly normalised db I would not expect to see stock as part of the material definition. current stock is no an attribute of the material. how you model it is upto you, but usually I'd expect to see transactions
x qty delivered 01/09/2014
Z qty to shop floor
Y qty to shop floor
w qty rejected and returned to supplier
... and so on
dont' store derived data
either store markup rate or sell price, but not both (one can be derived from the other + purchase price
I'd rather be riding on the Tiger 800 or the Norton