Any idea what this tea pot might be worth?

It's a coffee pot, not tea. See this one https://www.replacements.com/p/john...n-multicolor-coffee-pot-lid/jb_desbrm/9754341

Not old either - this pattern was made from 1962 to 1974. Ignore the replacments price (if there is one) and search eBay for Johnson Brothers Devon Spray.

 

I tried looking and I can't find another one for sale. Any idea how old and how much it would be worth to resell?

 

Scarcity does not necessarily imply value in this case. I already told you how old based on when the pattern was active.

Look to see whether other pieces of this pattern are listed or have sold to see whether there even seems to be interest. Beyond that, I don't personally have a clue.