Simple 4 item shopping cart solution

THIS PROJECT HAS A 2 DAY DEADLINE IF YOU CANNOT COMPLETE WITHIN THIS TIMELINE PLEASE DO NOT PLACE A BID. ALSO PLEASE BE ABLE TO PROVIDE A LINK TO A SIMULAR PROJECT YOU COMPLETED ALSO PLEASE READ CAFEFULLY AND IF YOU CANNOT PROVIDE ALL OF MY REQUIREMENTS DO NOT BID, I ALREADY HAD SOMEONE TRY AND ENDED UP PUTTING ME 2 DAYS BEHIND. My site was created using Joomla Currently I sell only 4 Items 2 services 2 Products. I am signed up with paypal and would like to use any open source shopping cart that will allow me to accomplish the following: Here are my requirements: During check out someone adds a product or service to the cart software they will have will be offered a related Product or service. They will also have the option of using a coupon code. At this point they have items in the cart And have the option to checkout or continue shopping. If they choose to check out the only have 2 options: option 1. If they have an existing paypal account they can enter there existing email address and paypal password. option 2. They will not need a user name password nor will they be asked to signup for any account, all they will need is there credit card information which will be via a form on my site. The client is to never leave my site During the whole process. Now my 2 products are downloadable Items so if they purchase a downloadable Item after thepaymant transactions is complete and verified they are to automatically receive an email with a link to the file down load. If the purchase does not include a any products and only services they are not to receive the download link, the email will also inform them that they will receive there license key within 3 hours which I will manually email to Them.