I tried Rules like explained here enter link description here. It works but when it comes to checkout, order total amount displays 0. I've got no clue why. Here is my rule:
{ "rules_sale_price" : {
"LABEL" : "\u0426\u0435\u043d\u0430 \u0441\u043e \u0441\u043a\u0438\u0434\u043a\u043e\u0439",
"PLUGIN" : "reaction rule",
"OWNER" : "rules",
"TAGS" : [ "sale price" ],
"REQUIRES" : [ "rules", "commerce_product_reference" ],
"ON" : { "commerce_product_calculate_sell_price" : [] },
"IF" : [
{ "entity_has_field" : { "entity" : [ "commerce-line-item" ], "field" : "commerce_product" } },
{ "entity_has_field" : {
"entity" : [ "commerce-line-item:commerce-product" ],
"field" : "field_produkt_sale_price"
}
},
{ "NOT data_is_empty" : { "data" : [ "commerce-line-item:commerce-product:field-produkt-sale-price" ] } }
],
"DO" : [
{ "data_set" : {
"data" : [ "commerce-line-item:commerce-unit-price" ],
"value" : [ "commerce-line-item:commerce-product:field-produkt-sale-price" ]
}
}
]
}
}