user upgrades: factor out gold/platinum prices.

app/controllers/user_upgrades_controller.rb

@@ -30,13 +30,13 @@ class UserUpgradesController < ApplicationController
 
     if params[:desc] == "Upgrade to Gold"
       level = User::Levels::GOLD
-      cost = 2000
+      cost = UserUpgrade.gold_price
     elsif params[:desc] == "Upgrade to Platinum"
       level = User::Levels::PLATINUM
-      cost = 4000
+      cost = UserUpgrade.platinum_price
     elsif params[:desc] == "Upgrade Gold to Platinum" && @user.level == User::Levels::GOLD
       level = User::Levels::PLATINUM
-      cost = 2000
+      cost = UserUpgrade.upgrade_price
     else
       raise "Invalid desc"
     end