getting equipment

im currently deciding wheather to buy this 9 piece boxing kit from ebay

http://cgi.ebay.co.uk/ws/eBayISAPI.d...166021365&rd=1

but im worried that the bag isnt heavy enough, i want a strong and heavy bag so i can work up to it and not start of with a light bag and then change it later on.

if its not any good anywhere else to go to buy heavy bags?

if it becomes so light that the bag is swing back and forth you can tie weights to the bottom. thats what i did with my 70lb bag i was hitting it so hard it would swing like mad so i tied 100 lbs of weight to the bottom and it stays still no matter how hard i hit