Vtiger products module customisation

I need to customise a standard vitiger 5.21 installation so it can handle our products & pricing structure (possibly using pricebooks?).

Our products have 3 pricing structures - retail, distributors & wholesale.

The pricing structure for each group is a discount based on the standard retail pricing.

Within each pricing structure, each product has mulitple quantity discounts -

e.g.
Widget 1 on the retail list
£7.50

Widget 2 on the retail list
£26.70

widget 1 in the distributor list
5% discount on the retail price if selling 1-3 items
10% discount on the retail price if selling 4-10 items
20% discount on retail price if selling 10 or more

widget 2 in the distributor list
2% discount on retail price if selling 1-5 items
5% discount if retail price if selling 6-8 items
10% discount on retail price if selling 9-15 items
15% discount if selling 16+ items

and
widget 1 in the wholesale list
6% discount on the retail price if selling 1-5 items
15% discount on the retail price if selling 6-10 items
22% discount on the retail price if selling 11 or more

widget 2 in the wholesale list
5% discount on retail price if selling 1-5 items
7% discount on retail price if selling 6-7 items
10% discount on retail price if selling 8-20 items
15% discount if selling 21+ items

There are around 500 products

I would also like to link to each customer's price structure from the accounts page so that when an invoice (or quote or SO) is created for that customer, the correct discount is applied for that customer/item and quantity

The standard retail price and the discount amount for each item must be shown on the invoice, the invoice is already customised exactly as we want it.

Please do not bid unless you can show that you have worked on vtiger customisations before