Problem with Clearing Codes for Emission Test

I own a 1998 Volvo turbo wagon (V70 GLT). I love it. I love driving it-the way it handles and feels a part
of me. But our love affair may be ending. It's got 120k on it, and it's getting expensive to repair. We
bought it used a few years ago with 68k on it. Mostly suburban, some highway driving. Thing is, I
cannot clear these codes (I know nothing about cars, btw). 2 years ago, the code was an oxygen
sensor-replaced ($$) and passed emissions, no problem. Now this year, it's Evap codes--it was a major
leak; repaired, only to have the timing belt need to be replaced, immediately followed by the mass air  
filter/sensor failing; got that replaced. Now instead of 3 codes, there are 5 incomplete. I am not sure
what they are (sorry). Mechanic says to drive around on the highway etc and come back. I do so, only to
have no change. So, finally my question: the ABS light has been going on and off, although the brakes
(which have been replaced about 2 years ago) work fine. I read somewhere online that the ABS being
wonky might interfere with these mysterious codes. What should I do? Have the ABS looked at/replaced?
I'm not made of money over here... I want to keep this car--for what I use it for, it's perfect and I can't
afford a car note at present. But this is getting expensive... Help!