Quote Calculator for Joomla. Image Attached

I have a website which we are working on at the moment (but is not finished) [login to view URL] The website advertises telephone systems for businesses to view and call us to hopefully buy. I have attached an image which roughly outlines what I want to happen. I want the user to see a box in front of them that shows the following NUMBER OF EXTENSIONS [ ] NUMBER OF TELEPHONE LINES [ ] When the customer fills in these 2 simple questions, it will produce a quote based on information which I assume we would complete in the back end of the system. If a customer selects 4 extensions / 2 telephone lines then answer may be SYSTEM A If a customer selects 20 extensions / 6 telephone lines then answer may be SYSTEM B Basically, each telephone system is made up of a series of cards which you add based on what the customer wants. I basically want this joomla extension to work that out and display the information as a pop up in front of the customer which then shows our telephone number. The Joomla extension also needs to show the price to the customer in three different ways 1. CASH PRICE (whatever the cost is) 2. 3 YEAR LEASE (basically a calculation of COST / 1000 * 107 / 3 = MONTHLY COST 2. 5 YEAR LEASE (basically a calculation of COST / 1000 * 68 / 3 = MONTHLY COST I know there are very similar extensions already about but I want something that looks right and works exactly how I would like. I have attached a very simple image of what I would expect it to look like (very basic). Is this something that can be done for me using something existing or something custom written?