Well definitely not the $150,000 range! haha
I'm not a professional by any means, more a hobby photographer but I've been told I've got some good stuff. So I think anywhere between $500-$1500 or so, give or take.
If you're leaning towards the d-SLR market and the versatility of interchangeable lenses, the lenses you have are somewhat more important than the camera. At any rate lenses don't change as often, or depreciate as fast/often as cameras do.
Canon and Nikon have about equal shares of 85% of the d-SLR market. Pentax, Olympus, Sony, Sigma, Fuji and others split the remaining 15%.
Nikon seems to have a technical edge over Canon at the moment and all the camera companies should be showing new products next month at a large yearly trade show.
Entry level d-SLR's are sold with kit lenses that are fine for amature use. More capable d-SLR's can be bought without a lens (body only) on the assumption the buyer already has a selection of lenses that will work on the camera or so a buyer can get a lens having a higher quality than a kit lens.
Kit lenses are the least expensive, camera makers offer mid-range price range consumer lenses that can cost from a few to about $1000, and professional quality lenses that can cost from several hundred to over $10,000 each.
Any Nikon lens made since 1959 will fit on any Nikon camera made today. Older lenses won't have all of the auto functions available today but they can be used manually to make images. Nikon uses the F-mount
Canon changed their lens mount in 1987 or so. It's the EF-mount and they introduced a second mount, the EF-S in 2003 that is for use on their entry level cameras only. I'm pretty sure, Canon EF-mount lenses can be used on
any Canon SLR camera made since 1987.
I use Nikon gear myself.