Struts or endlinks are likely the clunk, either way no biggie replace both and be good for probably the rest of the life of the car. The cat code, if it is indeed that, just do the non-fouler trick to trick the computer into thinking its fine, or replace it, another thing that wouldn't be replaced ever again.
So:
Struts: $200-$300 for Stock/KYB Replacements, $350-400 for Tokico HPs
Endlinks: $80 for all 4, $15 for vice grips to assist in taking the old ones off
Timing Belt: $100-$150 if you do it yourself
Cat: Pricey, or find a good used one, plenty out there from people who replaced them with a header at low mileage.
Non-Fouler: $5 and maybe $3-4 for a drill bit
so $500-$600 invested plus cost of car for a decent daily driver that won't give you too much trouble. I say worth it.