The construction price is an important parameter when designing neutron guides, but it has so far difficult to take into account during the overall optimiation. We therefore introduce the CoatingWriter add-on for the guide design tool guide_bot under McStas. This add-on allows for optimization of guide coating (m-value), taking both performance and price into account, in addition to the geometry optimization provided by guide_bot. We find that by using CoatingWriter we are able to generate good guides at significantly lower overall price levels than was possible before.