Ok, just to confirm what everybody has been saying:
--Killing the tax collector, baron(ess) and other nobles doesn't end the economy (I tested it)
--Turning economy off in the init file does not end the economy if the economy has already started (tested it)
--Turning the economy off or on affects what happens when the baron(ess) and/or tax collector first arrive. If it is on or off, the economy will respectively get turned on or off. There is no way to turn it off when it is already on, and I suspect there may be no way to turn it on if it is off (someone confirm?). This may be considered a bug.
--So, in conclusion, if you don't want economy, make sure that economy is turned off in the init file before you build your fort
Finally, like many players, I don't find that economy is really a good thing for the fortress. It seems like it will be a cool feature once it is fully fleshed out, but as of right now it seems kind of incomplete.
The main reason for this is there is no "legitimate" way to get the dwarves enough money to afford their rooms. There are some easy exploits you can do, but what fun is that? A side annoyance is that the message window will constantly get spammed with price adjustments, as each noble seems to adjust prices constantly and there are quite a few nobles.
Exploits to get dwarves money include:
--Build a lot of levers, don't connect the levers to anything. Assign the "Pull the lever" job, with repeat turned on. Each time a dwarf pulls a lever he gets money. Each lever can easily get pulled hundreds of times.
--Create unnecessary hauling jobs (someone confirm that hauling jobs pay money?)