First of all I ask have you owned the car since brand new in 99, or
have you brought it used? If used, where did you buy it? Dealer,
private seller, friend or relative? You DO need to realize that the car
is already 16 years old and everything you mentioned are regular
wear and tear maintenance items on almost every car. How the car
was driven and maintained during it's lifetime has everything to do
with how much work it needs. Having said that, do you do your own
repairs or pay someone? I ask because you say you changed the
O2 senor because the Ceng light was on. Did you have the car
checked for trouble codes before changing the sensor or was it just
a guess? If it was because of the code that's fine, but just because
you change the sensor, that doesn't mean that is why the light came
back on. You need to have the car checked for stored codes which
can be done free at almost any Auto parts store chains like
AutoZone, Advance, O'REilly's etc. When they read the codes, write
down the code numbers and what it gives as the code definition,
and in the exact order the codes are listed if more than one. Post
the results here and we can walk you through the repairs needed.
All the controls on more modern cars work in series with each other
so you could have multiple problems, and when fixing them you
start with the first cause(code/part listed) and then clear the codes
and redrive the car so that the system relearns. Sometimes you will
get more codes other times you have fixed it on the first go round.