I've looked at a bunch of units, and PROBLAST looks like it makes a high quality unit that will blast with anything, but it runs around $8k. A professional blaster will do the whole car for around $500-$700, so that will save you a lot of money unless you want to do at leat 10 cars, or you want to get into the business. I found a guy with a mobile rig that will even come to my place to do the job.
As far as the media goes, I originally was going to go with soda, but then decided against it. From everything I've read, soda and phosphates make a real mess, and can act as a paint release agent unless the car is cleaned with special solutions, several times, really, really well, to remove any residue. No matter what media you use, it will get into places that you just can't get it out of, but it will come out over time because of vibration. The big disadvantage of soda, is that it can react with water, so when it trickles out of someplace, and gets moist, it can cause severe corrosion.
One other concern that might affect your decision is the environment. If you have the blaster come to you, soda can be used virtually anywhere because it is biodegradeable, and harmless. Plastic, and other such media, on the other hand, needs to be cleaned up, which can be time consuming and expensive.
I ultimately decided to take my car to the blasters shop, and have him use plastic, when the time comes. That way, I don't get any of the disadvantages of soda, and he has reclamation equipment to do the cleanup automatically.
