How to display picklist values based on Lookup value on VF page in Salesforce?

I created a custom VF page to create custom object record. I have a Account lookup on page.

So whenever a user selects value from the lookup I would like to show dynamic picklist options on VF page by querying with LookupID for example I want to show names on dropdown, queried from selected lookup Id before saving the record.

Class:

public class createPriceRecord
{
public Price__c price{get; set;}
public Price__c priValue;
public Id lookupId{get;set;}
public Price__c ReqOpp;

public createPriceRecord (ApexPages.StandardController controller) {
price= (Price__c)controller.getRecord();
stdCtrl=controller;
}
private ApexPages.StandardController stdCtrl;

public void AccPopulated()
{
priValue= (Price__c)stdCtrl.getRecord();
}

public List<selectOption> getselectValues()
{
List<Prod__c> relatedprod = new List<Prod__c>();

relatedprod = [Select Id,name from Prod__c where AccLookup__c.id =: priValue.Account__r.ID ]; // trying to get Account id from VF page

List<SelectOption> Options = new List<SelectOption>();

Options.add(new SelectOption('','-None-'));

for(Prod__c prod:relatedprod)
{
Options.add(new SelectOption(prod.Id,prod.Name));
}
return Options;
}

public PageReference SaveRec(){

price.Look_Up__c = lookupId;
insert price;

PageReference p=new PageReference('my.salesforce.com/'+price.Id);
return p;

}

}

Page:

<apex:page standardController="Price__c" extensions="createPriceRecord" tabStyle="Price__c">
<apex:form >
<apex:pageBlock title="Price Edit" mode="edit">
<apex:pageBlockButtons>
<apex:commandButton value="Save" action="{!SaveRec}"/>
</apex:pageBlockButtons>

<apex:pageBlockSection columns="2" title="Price Information">
<apex:inputField value="{!price.AccountId}">
<apex:actionSupport event="onchange" action="{!AccPopulated}" immediate="true" />
</apex:inputfield>

<apex:selectList value="{!lookupId}" title="Select" multiselect="false" size="1" >
<apex:selectOptions value="{!selectValues}"/>
</apex:selectList>

<apex:inputField value="{!price.name}"/>
</apex:PageBlockSection>
</apex:pageBlock>
</apex:form >
</apex:page>