I don't mean to be a naysayer
about the horrors of sandblasting/ bead blasting...nor am I saying give the work to anyone with a sandblaster and a bucket of sand...but has anyone actually blasted a hole through a tubular frame with a sandblaster? I have been cautioned about this before, but went ahead and had it done at a professional blasting shop to an early 90s beast.
I asked the guys about it before I turned the frame over to them and their response was "we do this all the time with aluminum framed bikes and never had a problem".
I don't know how aggressive one would have to be to burn a hole or weaken the frame, but this was 4-5 years ago. This bike is still being ridden, albeit mostly trail/path by my wife. My 9 year old now rides it too with a bit more aggressiveness. Certainly voided the warranty, but I think the only way to refinish a Cannondale without voiding the warranty is to send it to the cannondale factory for refinishing at nearly the price of a new frame.
In reference to the original post though, sandblasting won't give you a polished look. It will look raw. I went this route prior to powdercoating. If I wanted a mirror finish, I would strip the frame with a chemical stripper, then wet sand with fine paper, then use polishing compound. It will take a long time to go from the brushed/sanded look to a mirror finish.
I just finished building up a polished dale frame that I bought on Fleabay a couple months ago. It is a factory polish that I had to re-polish it because the mirror finish was really dull from time and use. I used automotive chrome polish and it worked nicely. It took about 2 hours to rub it out by hand. I applied new decals to finish the job. It didn't turn out 100% perfect because there were some blemishes I couldn't polish out, but it looks real nice.