Adding a monthly payment option to our Magento site

We are looking to add what we call an "Easy Payment Plan" (monthly payment) option to our existing website and are looking for someone to add this facility.

It's a fairly small store with basically around 40 SKU's, but increasing to about 70 when all different size options are taken into account. The business is a hairdressing scissor company and the website is www.hairdressers-scissors.com

At the moment customers can only buy the scissors by paying the whole amount in one go, but we want to add the functionality for them to pay a deposit and then the remaining balance over the next 12 months.

The payment term will be fixed and not flexible and if a formula can be built into the system for working out the monthly cost this will help for if customers order more than one item at a time.

We are open to suggestions and ideas on how this would work best, but this is how I see it at the moment...

- The option to spread the cost of their purchase over 12 months only 'kicks in' when there spend is £247 or more.

- No matter what the total spend is over £247 they always pay an initial payment of £100 and then the remaining payment is split into 12 equal monthly payments PLUS 10% and then rounded UP to the nearest 50p

- IE, £247 - £100 upfront = £147
£147 / 12 = £12.25
£12.25 + 10% = £13.48
Monthly payment = £13.50

That is basically how we would envisage it working, but the most important thing is in how it integrates within the existing site and it's easy of usability and understanding for the customer.

If you are bidding for this work and have examples of previous work you have done providing this functionality to a Magento e-commerce site then please do give examples and links. Or to a working example on another website you know you could implement on our site.

We know how it looks and works in our head, but it would be great to see it in reality and this will greatly help us in the selection process.

We are looking for an immediate start on this if possible - depending on availability of best bidder.

Many thanks,

Alan