Build a Website incl. goldprice calculator as a plugin

We would like to add a scrap gold value calculator similar to these ones to appear in the right hand column on every page. The best way to incorporate the form would be something we’re happy to be advised on. Two examples of what we mean are contained below. [login to view URL] [login to view URL] There are 2 parts to the project. The first part involves creation of a form that asks user for - The weight in grams of their scrap gold - The quality in carats of their scrap gold - A calculate amount button - Display the approx value in pounds the user would receive that day from my client’s firm How the value is reached is the second part of the project. There are a number of carats with each one a percentage of purity and thus value. In addition my client, as a gold buyer, will take his commission which is a fixed percentage. To reach the result you will need to read an xml feed here [login to view URL] and extract that day's ask price for gold per gram in GBP. The value there is for 24 carat or pure gold. There are a number of other carats with the value percentages below: 24 carat is 999 or 1000 (essentially is pure) 22 carat is 916.6 fine 18 carat is 750 fine 14 carat is 585 fine 10 carat is 417 fine 9 carat is 375 fine There are 4 variables involved in each calculation 1) The gram weight of user’s gold (float) 2) The day’s ask price for a gram of pure gold [login to view URL] (float) 3) The quality/carat of user’s gold (float) 4) The commission charged by client. (float ) Example 1 - Site visitor comes to website and accesses the gold calculator. They have weighed their scrap gold and it is 16 grams. They check its carat and it s 14 carat. My client offers 70% of the current market rate. (current ask price is 35GBP/gram from [login to view URL] ) Calculation: ( Weight in grams 16 multiplied by days gold ask price) - ( reduction for quality/carat ) - (reduction for client’s commission) = (weight 16g x days value 35 GBP ) ( multiplied by .585 ) ( multiplied by .70 for client’s commission ) = (16 * 35 ) * (.585) * (.70) ) = £560 * (.585) * (.70 ) = £327.6 * ( .70) = £292 The value displayed to the user is £292 Example 2 User enters 11 grams at 22 carat quality. They then press calculate button. The days ask gold price per gram is 32GBP. = (weight 11 x todays ask price 32 ) x ( 0.9166 carat quality ) x (commission 0.7 ) = ( 11 x 32 ) * 0.9166 * 0.7 = £225 Example 3 User enters 55 grams at 18 carat quality with ask price of that day of 28GBP. = ( weight x todays value ) x quality x commission = (55 x 28 ) x .75 x 0.70 = £808.50 Additional The form will not need styled. Someone else will style the form at a later date. ---------------------------------------------------------------------------------------------------------- this is planed as a wordpress page the calculator needs to be a plugin thanks