Task. A house builder (invented for this demo) loses visitors who come for a price, can't find one and leave, while the manager answers the same questions again and again. The site is in Russian, for a builder in Russia.
Solution. A one-page site with house designs showing area and a starting price, a price calculator, build stages, FAQ, a quote form and contacts. The calculator updates as you choose area, floors, walls, finish level, roof, foundation and a septic system, and the slab foundation is priced from the house footprint, not the total floor area. One button copies every chosen option and the total into the enquiry, so the manager sees the calculation and doesn't have to ask. All prices sit in one settings file and can be changed in a few minutes without touching the code.
On a live site the enquiry is saved, sent by e-mail and to Telegram, with a consent box and a privacy policy under Russian data law. It works on a phone, has a dark theme, and the home page weighs about 100 KB. An automated test checked three calculator results against the formula.
