PHP, MySQL, jQuery web programming help

Website requiring development to enable release of a private beta.

Project:-
e-commerce store for downloadable goods.

Initial work needed:-

Improvement of add / edit product functionality - members sign up to the website and are able to add their own downloadable products for sale - this needs to be very easy to do - as to not put the member off listing their products on the website. Any products added need to be held for moderation by site admin. Products need to have multiple files for download upon purchase of the goods - as well as a sample download which is for free.

jQuery work to enable easy updating of the members "my products" page for product details that do not require review by site admin (i.e. price, availability, etc)..

Custom shopping cart checkout - currently products are added to a custom shopping cart (running from a MySQL database). Need to fully integrate a payment solution to take the products in the shopping cart - accept payment by the member - and then update the MySQL database table to show that the products that have been checkout should now be available for download by that member and that member only.

Needs a restriction on the shopping cart of a minimum value of total transaction of $1.00 say (before tax). This is so the website can sell products at prices as low as $0.01 - the members would have to buy 100 products at $0.01 before they are able to checkout the products