you are so lost , lets simplify it
the price in your source is the actual price
the price in itemtype.dat in the client is the price showen on client
so if at your itemtype.dat the price of expball is 27 cps , and the price on source is 54 cps then it will take 54 cps and not 27 cps
and if the price in your client is 2700 and real price in source is 27 then it won't buy it until the client have that 2700 cps (client side check) then it will buy it for 27 cps which is the source price
how to edit the itemtype.dat ? search buddy :)
even search for item you know it's price and you will find it :) price is at offset 37
how to add it to some shop or something ?
eshop , shops at both client and server
it's pretty confusing for me sometimes but what i do is
do whatever edits on client side , copy files to server side
you should know the id of the shop you editing (maybe try to guess it by comparing items in shop in game and in file) and the mall was 2888 as far as i remember :)
so again , go to the item you want to edit , edit the price at offset 37 , done
goodluck
edit :
you better to get the item price at source from the itemtype in the source , so it will make it way easier to edit the itemtype then copy it to client and it shows everything (that's what i actually do)