RE: is there a minimum sales price for the item in AX 2012 R3

as I remember in AX2012R3 there is no such direct functionality. But you can get it done via customization .we had same kind of requirement to control Item Price Discounts not  to exceed Item cost price.

So if you want to implement this on POS you will need to Customize Realtime Service and related components.

Hope this will help.

Thanks & Regards,

Amith Prasanna