I must say that there are loads of 737-300s around, and it is such a great aircraft. I have recently done quite a few jumpseat rides in 733s and it's such a delightful aircraft for a pilot, and probably a five year old 733 is half the price of the 736, which I guess is a kind of "entry-level" 737NG. I know the 733 is a little bigger but it's definitely cheaper. It's just a classic workhorse and way too soon to replace it.
Someone who said the 100-seat market is sluggish now is right, plus the waters are muddied by contradictory competition, ie stretched RJs, EMBs, Avros, A318 et al. Not to mention Boeing's own 717 - what is the point of this plane? Unless you're Air Tran? If you're going to invest in new technology, it should be the start of a new line, not the end of an old one (depreciation on 717-200s will be twice that of any 737 or A318-21).
fly Saha Air 707s daily from Tehran's downtown Mehrabad to Mashhad, Kish Island and Ahwaz