Rolli's suggestion of GTS 250 is indeed the best you can get for $70 and faster than a 9800GT and HD5670.
So you can get that.
But on the other hand you have a CRT monitor so you'll be fine even with 9800GT as it can display lower than max resolution without any blur unlike LCD monitors.
With my own experience I can say that 9800GT can play most games at 1600X900 decently (and even higher).
So if you can't go above 60$ then 9800Gt will also be fine.
But If you can, then get GTS250 for $70.
And your PSU is enough for any single GPU so no need to worry about that