A Mac for University

Hey everyone! I'm heading to University next year, and need advice of which option to take out of these. At University, I'm doing a Bachelor of Information Technology and a Bachelor of Arts (Japanese). (Note: All of these prices are in Australian Dollars)/

Option 1: Upgrade my MacBook

I've got a MacBook (mid-2010, Polycarbonate) which is in okay working condition. It's still running Snow Leopard because my school is stupid and won't let me update to Mountain Lion (I've purchased a copy). After leaving, I could upgrade to Mountain Lion, upgrade the RAM to 8GB and upgrade the HDD to a 512GB SSD. This would cost me about $600, though there is some physical damage to the MacBook and it would still be quite heavy.

Option 2: Buy a MacBook Air

I could buy a 13-inch MacBook Air and upgrade the RAM to 8GB myself. The computer costs $1500 stock, but only comes with 256GB Flash Storage. Upgrading to 512GB of Flash makes the price $2000, with a further RAM upgrade costing about $100. This obviously costs quite a bit more than the upgrade option, but it'll be brand new and will weigh a lot less than the current one.

Option 3: Buy a Retina Display MacBook Pro

I could buy a classic MacBook Pro, but if I'm going to go with a Pro, I think I'm just going to stick ahead and get a Retina Pro due to weight again (I'll also be carrying a Surface RT around with me). This base model 15-inch comes with 8GB RAM, but still only 256GB Flash Storage. Upgrading to 512GB adds another $500 again, bringing the price to $2700.

Which do you think I should get? By the way, if you're wondering about the 512GB of Flash, I need that amount of space because this will be my main computer with the addition of a monitor. Thanks for your help in advance!