Have a look at the uprgrade prices from Maxon before buying to make sure you understand their policy. It can be quite pricey.
As far as the the XL version selling for 1800$, I would think it would be the latest version ( 9.5). Buying 7,3 XL for that price would be just a huge rip-off!.
If you are in the US, check out the prices at http://www.novedge.com ( tip from AdamT), they sell the XLbundle (9.5) for ca. 1200$.
If you are just trying out for now, there are a lot of free programms out there as well, such as wings3d, or blender which are quite to learn the basics ( Wingsw is also in general a good polyon modeller).
v7.3 is missing a lot of the workflow improvements/modelling tools that I like about Cinema4d. It still is a good programm, and has things you won’t get in the 9,5 core release ( well, radiosity and caustics…).
I would still rather go with 9.5 Core if you can afford it.
It is just much more evolved.
jp