Create HTML code to allow users to calculate costs

HTML to allow users to enter data and choose several options that will give them the cost of that option. How many people age 5 years and above. (enter a number). Meal option A (7 meals) or B (8 meals) - pull down menu. Cabin rental or Yurt rental. Activity fee. This will be a set amount x number of people over age 5 and above. There will be a minimum number of people per housing option, so if their number falls below that threshold, they will have to pay that threshold amount. Every person above that threshold adds a set amount. I will supply the minimums and amounts. I will supply a screen shot example of how I'd like the entry boxes and results to look (nothing fancy). My website is in HTML, so it will need to something I can just insert into the page. It will also need at least some documentation so I can change the parameters in this coding, if the costs change.