Cost

Costing:  No cost estimate is required - Felton will be able to assess by eye whether a proposal is going to be "cheap, average, or expensive" to make, and that will be enough for them to decide which ones to pursue - they'll do their own detail costings at a later point in the process.  Having said that, you shouldn't ignore comparative cost issues in doing your design:  all other things being equal, cheaper is better.  In this sort of design, you won't have a lot of latitude with the amount of material involved - most of the cost variation is going to come down to the labour to form it and assemble it, so focus on that.