I remember my first SLR, an Olympus OM-2n, which my dad bought for me back when I was around 14. It cost under $300 at the time and the comparable Nikon was the F3 and that sold for around $450. That's a far cry from the cost of the first DSLR. Back in 1991, Kodak came out with the DCS, which was a digital SLR built into a Nikon F3 body with a whopping 1.3 megapixel sensor and with all of the digital camera electronics, it was double the height of the film SLR. When the first retail models became widely available in the market, it sported a 6 megapixel sensor, was called the DCS 460 and sold for $28,000. By the late 90's, Kodak also came out with a line of DSLR's that were based on the Canon EOS-1N (to target those customers with all their money invested in Canon lenses) as the DCS 560 and that one sold for $28,500. It wasn't until 2000 that Canon decided to come out with their own DSLR's under their own name with the release of the D30, which sported a whopping 3.1 megapixel sensor. This was the first DSLR that sported the digital camera capability in the same size SLR body as a film camera. Nikon quickly followed suit and this pretty much coincided with beginning of the end for Kodak.
From then until now, both companies have come out with new models across their "amateur", "advanced" and "professional" lines pretty much on a one to two year product cycle.
Nowadays, even the view format cameras like Mamiya and Hasselbad also have digital camera backs that can be used with their cameras, but those run in the $10,000 to $15,000 range.
And I still remember the first digital camera I ever bought.......a Sony camera with a 640k pixel sensor with a built in 8 MB memory. I think I paid almost $300 for that.