(1)Merchants sell you objects for more than their price and buy them for less, plus iron is more valuable than bronze. And your starting gear isn't well crafted. So you're probably down by a decent amount of coins.
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(2)You could also take items from a warehouse, castle, house, or shop (I'm not sure about that last one though), as I don't think people get mad at you for theft currently.
(1) While that is certainly true in dwarf mode, last I knew merchants sold items for their exact value in adventure mode (did this change for DF2012 and I didn't notice?). The value of an iron short sword with base quality should be 60 (assuming I did the
math right). I vaguely recall this being about the value too - I'm pretty sure 238 should be more than enough to buy one. You can pay the merchant the minimum value by offering them 1 coin, and then trying to trade - they will counteroffer with the minimum value they are willing to take. Similarly you can ask for 9000 when you sell, and they will counter with the actual value.
One thing which confuses this is that merchants will not give you face value for coins that are not used locally. In other words, if you get "lala happy elf silver coins" (not a real name - I can't remember any actual DF coin names) from merchant X in on city, they won't be worth as much if you try to buy from mechant Y in a different city that uses different coins, you won't get the full value for them (I think you get 1/50th the metal value, according to the
wiki). However, you should definitely get full value if you try to buy something with coins you got from the same merchant (again, assuming this hasn't changed recently).
(2) DO NOT STEAL FROM SHOPS!!! You can take all you want from castles, warehouses, etc. However, items in shops will show up as $iron short sword$ etc. If you take anything with $$ around the name out of a shop (i.e. things you haven't paid for) you will become an enemy of the civilization, you won't be able to fast travel until you get out of the city, and everyone will attack you. Also, the stuff in shops tends to be inferior to what you can find for free in castles anyway, and shops won't have armor and several other necessities due to
bugs in this version.