My very first gun is a Five Seven. It is a great gun. Very accurate, light,and reliable. It is the gun I carry whenever I can carry. Ammo can be expensive if you don't buy it in the right place. I have seen it as low as $18 per box of 50 to $30 for a box of 50. Every once in a while you see someone trying to sell SS192 ammo for $100+ a box of 50 because it was supposedly banned because they are AP rounds. That is crap. That ammo was banned, and is severely overpriced.
You can also reload this round if you are into reloading. That will save the price on the price of ammo. Take a look at Elite Ammunition for some of their products (ammo and reloading supplies for this round). This round isn't as cheap as .22LR or 9mm, but if you search a little you can find the ammo at 36¢ a round. That is about the price of .45 and I believe .40. The $22 a box quote from another poster puts the price at around 44¢ a round which is also around the same price as .45 ammo.
I think once you shoot this gun a few times, you will really like it. Don't know if I would sell a P229, but I would definitely save up money to buy it as another gun.