The first two are reasonable ways of excluding very old cars... but the last one is a crap criteria.... and why you would quote the DC5's highway fuel consumption rather than combined cycle or urban where it's far more likely to be used is beyond me. I'm also going to presume you're looking at an Integra Luxury (non-R; and probably not even a Type S in the sub $20k price range).
EDIT: Considering your criteria is 2003 onwards, you won't be getting much DC5 for that money other than the Luxury model. Plus side I suppose is that it's unlikely to have been thrashed much but it's price would be inflated by the fact that they stopped making Integras and suitable sports-oriented cars in the $40k price bracket. I actually did consider buying one of these new back in 2006 but at $40k driveaway, it was a bit steep for me and I ended up with the Civic for $30k driveaway.
As for me? I'm not sure yet. Don't really need another car as I have both a DD and a track car, but I guess I wouldn't mind selling the DD (should get around $18-20k per Redbook) and then with $40k I could buy a late model 3 series (e92 pre-facelift 325i vs. e46 330ci).
EDIT: With $40k, I just realised I could even get a 2004 525i e60 (
http://www.carsales.com.au/all-cars...iceTo=415&seot=1&__Nne=15&trecs=355&silo=1011). I'd probably go for this over the e90 325i.
If I was really limited to $20k and wanted a new car, I'd probably go for the Mazda 2 with safety pack. I really enjoyed driving the Mazda2 and would keep the change. Alternatively I wouldn't mind a used MR2, a Skyline R33 perhaps (or an R34 GTT possibly if I could find one)... but I'm not a huge fan of used cars having had many friends get stung by these (mysterious repairs required) especially with performance cars.
