yes the outlaw class does race at imi. They will do about a 1minute lap compared to a tag wich will do a 0:55 or a 0:54 second lap. Yamaha kt100s are about a $1000-$2500 kart but the engine alone is about $750. My Margay chassis with out a motor is at imi right now for $900. It has a 35mm axel and worked great with a yamaha kt100. Compared to a tag wich is about a $3000-$5000 kart. A new tag motor is about $2900. I have found that there are a lot of tags in the $4000 range ready to race.
http://www.yamaha-motor.com/sport/products/modelhome/464/0/home.aspx
that is the yamaha kt100 page
If you chose to buy a yamaha kt100 new there will be some changes you will need to make such as the pipe and clutch.
thanks
fletcher