An NPC that offers specific service, either new item, item upgrade, or secret trigger, for cost that consist of multiple counters to be paid simultaneously. Stand on FFC and press Ex1 to render string and then cost (up to 6 different counters with separate cost for each). If you can afford, press Ex1 to confirm payment, or Ex2 to cancel.
If HP is used as part of cost, minimum of 1 heart must be left to afford payment.

1. Set up graphics:
TILE_CR_* for rendering counter icons using CSET_CR_* for shop UI.
3x3 frame for TILE_RESOURCE_FRAME. Needed to render UI frame using CSET_RESOURCE_FRAME CSet.
Combo for "Sold Out sign".
Combo for prompt display, when Link tands on FFC.
2. Set up constants in script file to match graphics you set up.
3. Place FFC st shop position.
D0-D5 - counter costs, for each counter:
#####.____ - ID of counter used to pay.
_____.#### - counter amount to pay.
D6 #####.____ - String to display as intro when standing on FFC and pressing EX1.
D6 _____.#### - ID of required item (taken away on purchase). 0 for no item needed.
D7 #####.____ - Screen D bit to track "Sold Out" status. >12 - infinite stock in shop.
D7 _____.#### - ID of item sold/upgraded into. If D7<0 - secrets trigger instead on purchase (cash gate, building construction).