Using Drop downs in creating an estimating worksheet.

Hi All,
I am creating an estimating worksheet for calculating the cost to produce dimensional CNC router cut letters. I am a nube at Excel and I've been studying up on the basics. Jeff was a big help with the formula for counting text typed into a cell.
To keep the user interface simple to use, I would like to use drop down lists to choose the options such as letter heights, substrates used to make the letters out of, and a number of others.
I've attached a sample file that better explains what I'm trying to achieve. I've inserted some dropdown lists into some of the cells as well as some basic formulae where I could.
At this point, I'm trying to combine an item from the drop down list with the cost per square foot for the material.
Once I get past this hurdle, I will continue to add to the formulae with optional items and minimums.
Let me know if you can help.
I'm loving working in Excel!
Duncan