Ok, take 100 japanese yen coin. Only this coins give you the right equal probability 50/50 then taking important decigions in you life. Especially then choosing japane camera.... I am just preparing you to choose between Nikon and Canon

LOL You can select another tool for solving Nikon/Canon delema. Better go to shop and see what you like more then in lies in your hand. If you can not choose one, try Sony
I will give brief pricing gude. So for you not ot get confused on
second hand market. Look. DSLR cameras are usually split into 3 classes. Top, middle, low and there is even 4th sublow. I will explain on example of Canon. Nikon have same categories but different digit notation.
Canon top have one digit -1D 1Ds 5D, middle have two digits 20D 30D 40D... budget 350D 400D 500D.... extra light (budget) 1000D etc
Then once in few years Canon increase megapixels, functionality, etc. Each time they usually encrease numbers in model name:
300D 6.3mpx Aug 20, 2003
350D 8Mpx Feb 17, 2005
400D 10Mpx Aug 24, 2006
450D 12Mpx Jan 24, 2008
500D 15Mpx Mar 25, 2009
550D 18mpx Feb 8, 2010
600D 18Mpx Feb 7, 2011
starting from 500D they have video feture. between 550D and 600D there was almost no changes. Actually there is nothing elese you probably want from camera and it become technically difficult to fit more MPX on this matrix size.
they cost maybe around 500 pounds new
Same with two digits line 10D 20D 30D 40D 50D 60D...
they cost below 1000 pounds new
And top line 1D 1D 1D 1D... oops we run out of numbers, so Canon added "mark": 1D, 1D mark2, 1D mark3. 5D and 7D a bit special line, not reincarnation of 1D. They stuck between 1D and x0D series. 5D got already younger brother 5D mark2.
They cost over 1000 new.
Top/middle/low can work well. But top line made for professionals make their job easier and most effective way. Low level not limiting your creativity, but some time take longer to get same result.
In your case i can see that you probably will choose from low and middle range. Higher level cameras usually have longer reincarnation intervalls, and loosing slower in price with the time.
But true, let us know budget and requiremet and people here are always ready to help