The only vacuum I absolutely LOVED was a Rainbow. It did it all...and more. Even skeptics were convinced when they saw it in action in THEIR home. (When I get "on" something...I tend to be anal. lol)
I had it serviced twice and replaced no major parts. It worked like a charm still ...after 20+ years. However, it had a power head with a beater bar...not so good on tile. I could have used a long wide brush-like thingie on tile...but I forgot about it...and gave the vacuum away when we went with all tile. Why so many details...don't want anyone to think I got rid of it because I didn't like it, or because it broke.
Anyway...it was over a $1000 bucks mannnnnnny years ago. I think it is a safe bet that it hasn't gotten cheaper over the years. However, the price may be worth it, considering how long they last and allllll the cool stuff it can do besides "just" vacuum. Since it gets to the deeeeeeeep dirt...saves wear and tear on carpets as well. If our carpet had been a different color (not a color from the 80's), people said they would have no idea it was as old as it was.
So, you aren't sold on a Rainbow...
What is under your carpet? Wood? Cement? There are options for inexpensive things a person can do to their flooring that doesn't involve replacing carpet, tile, or wood. I've seen people paint (special cement paint) their cement floors and it looked realllllly nice.
We went to all tile a few years ago. Even in the bedrooms. I was afraid I would regret it. I don't. I will NEVER have carpet again. We made a few "remodeling errors," but going with all tile wasn't one of them.
/rambling