Как-то так:
AddEventHandler("main", "OnAfterUserRegister", "OnAfterUserRegisterHandler");function OnAfterUserRegisterHandler(&$arFields){$newBudget = 100;// если регистрация успешна тоif($arFields["USER_ID"]>0){CModule::IncludeModule('sale');$arBudget = Array("USER_ID" => $arFields['USER_ID'],"CURRENCY" => "RUB","CURRENT_BUDGET" => $newBudget);CSaleUserAccount::Add($arBudget);}return $arFields;}