Hi stripes
That's definately a good idea. My Train Shop will incoroperate layout designing and eventually layout building too. I've got a layout design program, I designed a layout for this one gentleman to his specs and he was so happy he said he's considering contracting me to build the layout too- my first customer by the way (soon hoping to open my own proper one).
A lot of the time we have a customer phoning or emailing our shop (the one where I currently work) asking us to make up a custom starter set for around R500 (+/- $70) just to get them started.
So I put together a set consisting of the following: 1 x Co-Co Diesel (R250); 3 x flatcars (R45 x 3= R135); an oval of track (Consisting of four straights and twelve curves = R65) and 1 x Model Power controller (Very basic, just back and forward and speed @ R50) = R500.
Also, as a gesture, I give them a bag of free ballast which costs us just R15 ($2).
So, you can even go a step further and, as you want to, offer them a complete package- I suggest having an example in your shop as to what you can do. I made a small layout in three days for the model shop where I work- it's value excluding trains is: R3500 ($485). It consists of an oval of track (12 Curves, 6 Straights), a few buildings, figures, cars. The price includes a special table that was made by my bosses CNC Router company, everything just clips or slides together (you can offer these as well, since the excuse these days from people is: I don't have time for a layout.)
Who knew you could build the most basic of basic layouts in just three days?! Also, the more you are able to offer things according to their budget and wishes- as you're planning- the better for you and the more likely they WILL come back.
Just watch out for the dodgy ones- we have one customer we call "Petrol George", he phoned my boss and asked if we had any nice S.H. Marklin. My boss obviously said yes. So he threatend that if he drove all the way to the shop my boss would have to give him petrol money- my boss thought it was a joke and just laughed.
So this dude came to the shop and he spent two hours there, he found nothing of interest and said: "Right, I don't like anything, where is my petrol money?". My boss still thought he was joking. Eventually, after another hour, my boss gave him 100 bucks so that he would leave! And that's how he got the name Petrol George- needless to say he still buys stuff from us.