I admit to knowing nothing about lenses and would appreciate any help that could be provided.

Peewee suggests the 50-500...personally, I dont!
May seem attractive with the price...but the 500 end, it will be f6.3 (far to slow for wildlife!!!, need lots of light!)

The Canon EF300 f4 is NOT a tele but  a PRIME lens (Prime lenses are faster and optically superior to tele len 's!!....and a cracker of a lens at that!

The faster the lens (lower f number(s, 1.2, 1.4, 1.8. 2.8, f4, faster it focuses, locks on etc...the more one can expext to pay

I have the EF500f4 (£4000!!!) and the EF300 f4 (£1000) amongst others!!
You get what you pay for and imo, the results show!
Why put a sub lens on a 40D!?