What is a scope range that can zoom in at about 300yds?

Nikon
Bushwell
Maybe Leupold (somthing under 300$

A 3-9x40… Of your choice

unless you want to be able to count the fleas on a donkeys *** then you may want a 6.5-25x50 which will run at least $600

I don't think I'm going to be alone in wondering just what you're asking. It seems you may be confusing focus with magnification, two very different optical concepts.

Depending on how old your eyes are, a nice scope in the magnification range of 4 x 14 power would work best for you.
I have a 4x14 power and it works well at 250 yards and over.

The Leupolds are very nice, but will be very expensive --- over $500
http://swfa.com/...P2581.aspx
http://swfa.com/...12680.aspx

Bushnell 4200 is a nice one but they can be $400 to $500 or more as well:
http://swfa.com/...11606.aspx

I would highly recommend the Nikon BuckMaster. Excellent scope, and very clear glass optics. I think they run $290 to $350 or so. An excellent value in rifle scopes:
http://swfa.com/...42256.aspx
http://swfa.com/...42257.aspx

You have selected three really good brands of scopes. For use at 300 yards, I would recommend at least the 4x 14 magnification. But my eyes are older.
I would again highly recommend the Nikon BuckMaster for the high quality and value. The Leupold is nice, but is twice the price.

My son and I have both taken deer at around 300 yds with a fixed 4x scope, no zoom required.