A common form of game setup is to give each player a quantity of "money" of some sort, then give them a menu from which to buy things. The way you would implement this in Xconq is similar to the method for limiting unit quantities - make the money be an initial supply of a special material type not used for any other purpose. This initial supply should be given to a first unit that each player starts with. This first unit could be something like the adventurer in a fantasy game who starts with a pot of money, so the first unit is also the most important one, or perhaps a little dummy unit that buys the other units and then is of little interest thereafter, sort of like the national bank for the player's country.
Here's an example:
(unit-type adventurer (start-with 1) ) (unit-type shop (start-with 1) ) (unit-type sword) (unit-type armor) (unit-type boat) (material-type money) (table initial-supply (adventurer money 200)) (table acp-to-create (shop (sword armor boat) 1)) (table material-to-create ((sword armor boat) money (20 100 1000)))
The shop can't do anything besides create items when given money. The adventurer starts with the money and has to give it to his/her shop, then order the shop to create the items desired. The shop will create completed items instantly, ready for the adventurer to use.
Note that this can't be extended to buy extra intrinsic qualities, such as hit points or action points.