I play both but I lucked into an Empire deal ($75 for 2000 points, the dex and the fantasy rule book) and have added another 50 into it. If you have patience keep an eye out on Ebay and other trading sites.
Another option if you want to play IG you can cut your costs at the start by getting into the whichhunter or deamon hunters to start and then ally IG into them.
Another option if you want to play IG you can cut your costs at the start by getting into the whichhunter or deamon hunters to start and then ally IG into them.