@lechatnoir The reason dogs cost so much is because of the expectations that come with buying a well-bred one.
For instance, you mention the Cavalier. Lovely breed, but plenty of health issues. Naturally, if you want one, you want to lower the chances of these health issues happening. That is done through image and genetic testing.
These aren't cheap. A MRI that can detect syringomyelia (one of the conditions frequent in the breed) costs thousands. And, if syringo is detected, the dog should not be bred.
Other issues, such as Mitral Valve Disease, don't appear immediately. An echo is recommended every year for breeding Cavaliers, and because it can always show, you should wait a bit before breeding a pair to make sure it won't appear at an early age. As age increases, fertility drops. So you're potentially looking at small litter sizes (especially with small breeds!).
So you should expect a Cavalier to be very pricy. It is definitely not a breed to buy from someone who "just had a litter", because they won't have done the tests needed to increase the puppy's odds to thrive.
I can't find your post about other breeds you're looking at, but I remember your mention of toy poodles. It's worth considering that poodles, their crosses and drop coated breeds require grooming, which isn't cheap.
And speaking of crosses: mixing breeds isn't a revolutionary way of fixing issues. If you look for, say, a Cavalier Poodle cross, you should have each parent tested for issues known in their breed. I also recommend you have about doodles here: About Goldendoodles
Because of reasons mentioned above, as well as the basic rules of supply and demand, some dog breeds will cost more than others. Generally the Hound group will have some reasonably priced dogs, as they aren't fashionable right now but can make fantastic companions.
I recommend that you first decide on a breed. Then you can familiarise yourself with breeders, learn to tell ethical breeders from puppy mills, as well as learn more about the breed itself so you're ready when the puppy comes home. Good breeders often have waiting lists, and won't breed without one, so they don't risk still having an entire litter at 8 or 12 weeks old.
The best way to find ethical breeders is through parent club websites, which will often detail what health testing should be done. For instance, on Syringomyelia: Testing
Sometimes these websites aren't updated. In that case, I would send an email. Another good way to find good breeders is to look for dog shows near you. You could either go and watch or check the results online and google the prefixes of the animals there so you can get the contact of breeders.
Finally, as for breed suggestions that could help you, could you please tell me:
What size you're looking for (for instance, small usually goes up to 10kg, but toy dogs max out at 4. Most people think of toy dogs when saying small):
How much grooming and shedding you're willing to tolerate/do (combing every day, combing every week, taking to the groomers):
How much barking bothers you:
Energy requirements (a walk around the block or would you like to jog with your dog):
There are plenty of breeds out there, some of which desperately need new owners.