P0130 code problem for 1998 Legacy Outback

[firestix]

May I get some advice about how to address a specific ODB code problem?
I have a 1998 Legacy Outback with 127,000 miles on it ... My check engine light came on yesterday and I'm getting a code that reads: p0130 O2 sensor Bank 1 Sensor 1

Is it possible to be anything else than an O2 sensor, or what's the best way to more accurately diagnose the problem. I simply don't want to spend 140 dollars to find out it wasn't the O2 sensor after all.

Any help is greatly appreciated!
Thanx in advance!

-Firestix