Payment on Balances until paid

This is what I want:

1. The ability to import customers and have additional fields (in groups of two) that represents a balance and what the balance refers to, for instance:
   
   custname, custid, balanceItem1Name, balanceItem1Balance, balanceItem2Name, balanceItem2Balance, etc..
   
   
2. The ability to add items (a max of 20) to a customer
   
   
3. The ability for the member to pay on said balance until the balance is cleared
   1. member should have the ability to pay equal amounts for a set period of time
   2. member should have the ability to pay arbitrarily

Note the example below:
Customer goes to the furniture store today to buy a couch. The couch costs $1800. Customer pays $1000 and has a balance of $800. Customer is given credentials to log-in to aMember and make payments on his "balance". The balance for the couch I would refer to as balanceOne. At some point in the future the customer comes back and wants to buy a washing machine which costs $750. He pays $500 and gets his washing machine and has a balance of $250. The balance on the washing machine is referred to as balanceTwo. That customer when he logs in to aMember will see two balances referencing two different things; the $800 balance and the $250 balance.

Please let me know the cost to build this and the time it would take to create.

PS: In point 1 above, the comma delimited list is just an example. Of course I would want to use the same field specification as aMember default.