Website development in two stages

I have an existing NZ website which has full online trading functionality, however the UK site doesn't and instead there is a deep link through to an external retailer site for purchase.

I need two quotes and timing estimates:

1. A short term solution to implement shopping cart functionality on the UK site asap eg some kind of bolt-on to plug-in and link through to existing accountancy software, enabling customers to purchase direct

2. A longer term solution eg a complete overhaul of the site to refresh the look and feel of the overall customer journey