You may be happy to know that The Sims Medieval for iPhone and iPod Touch is FREE for a limited time only! It is part of a holiday deal from EA (wow how nice of them). Seeing as I wouldn't have known this if it weren't for one guy, credits to MTDM please! :)
You can also check this site for Daily Deals from EA for iPhone, iPad and Android-powered smartphones. The iPhone version of the game is 62.5MB, so it's relatively small for an app but you'll need to connect to a wi-fi hotspot to download it or download from your computer as 3G is capped at 20MB.
Here is the direct link that will open the application page in the iTunes Store.