Your poor mileage and poor smog results on your 240 are probably directly caused by your exhaust manifold leak.

It looks like you could sort this all out for about <$200 in parts.

Say $200-300 for labour and you're laughing. If finances are a worry, $500 for the car you already have is much more sensible than $3000 for taking on a 'new' used car (which I have found to be quite expensive in the first year of ownership). If you plan on having money in a couple of years, stretch the 240's life to get there and make your purchases then. I don't know where you are, but here in NB you'd pay ~$400 in tax to buy a car for $3000, and you can fix your current ride for about that much.

(some of this would be optional, I'm just listing it for an idea...)

Alignment - $70

Exhaust
manifold - ~$25
gaskets


From FCP:

tie rods - $10 aftermarket/$20 OEM

ball joints - $12 Aftermarket/$35 OEM

exhaust
gaskets - $10

Exhaust
manifold - $30
studs
and nuts