I am thinking its about time to change my 02 sensor I have about 125k on my 91 4runner 22re. I cannot rember if the previous owner changed it or not but my gas mileage hasn't been as good as it was. and its never idled that great sometimes it idles at like 2,000rpm's unless I blip the throttle then it returns down back to a little under 1,000rpm's like it should.
I changed all these things within the last year.
cap
rotor
air filter
spark plugs
spark plug wires
oil filter/oil every 3k

I'm thinking I should change vacum hoses.

should I get a new 02 sensor?
I have looked around at prices on them and they run anywhere from $40 to $110. I am assuming OEM the way to go? what is a good place to buy from? suggestions, warnings, tips tricks anything to do with 02 sensors that will help me out is greatly appreciated!

Cheers
R.