I'm currently in tray #18 (of 20) with Invisalign braces. I had metal braces when I was a senior in HS/beginning of college and wore my retainer for a few months afterwards (I also had a permanent retainer put on my top two front teeth and bottom 6 front teeth the day the braces came off). I have a LOT of cavities and unfortunately my retainer didn't fit after having some of those filled (it was a clear plastic retainer) so I stopped wearing it (no way, no how were you getting me into my horrendous ortho's chair again!).
Well, my teeth did OK for a couple of years and then they started to shift. The bottom teeth aren't too bad because of the permanent retainer, but the top teeth got all out of whack. The two that were held together with the retainer moved back towards my throat and the other teeth crowded forwards

. If the top 6 teeth would have been held together from the get go, I wouldn't be in braces now

.
As for cost, I only have them on the top teeth. They cost me $1000 (family discount since my brother is a dentist and he does my Invisaligns). I orginally had 20 trays (a new tray every 2 weeks), but DB wants to fine tune my teeth and make them perfect, so I'll be doing a few more impressions and a few more trays. At least DB will prescribe me a Xanax to take before my appts

to ease my dental phobia.
I know I'll be getting a clear retainer when I'm done (they can make them right in the office) which I find less irritating to my mouth.
As far as cleaning them goes, I get packets of cleaner with my new trays to use every 3 or 4 days. The Invisalign brand cleaner actually smells like bleach, and it definitely makes them sparkle.
Overall, I definitely have like my Invisalign experience better than the traditional braces, although I'm sure a large part of that is being tremendously more comfortable with my dentist/ortho. I ended up with lots of cavities when the braces came off, many of which were through the sides of my teeth where the metal bands were

. With Invisalign I can thoroughly brush and floss my teeth, which I couldn't with regular braces. The other nice point is that you can take your Invisalign out for an hour or two if you're going someplace where you'll be in a lot of photos (like at my other brother's wedding).
Let me know if there's anything specific I can help you with.