Those prices don't look too bad, but you can definitely piece it together for cheaper, particularly if you find a good deal on ebay or craigslist.
i definitely recommend larger tanks, as well as multiple tanks. the cost per pound to refill goes down drasticallyl as you get to larger tanks, 20 lb tanks are fairly common to find on craigslist, at least where i am.
the reason why i recommend multiple tanks, is that you will inevitably run out of co2 when you need it the most, and having a spare tank or two gives you flexibility for when you want to swap, and also the safety of not running out of co2.
also, as for the co2 tanks listed in the pages you posted, they are new tanks, which you are paying a premium for. you can find used tanks for a fraction of the cost. plus this way, you won't be shocked when they just take your tank and give you another used one... some places fill on site, but here in Austin, most places send off their tanks to get filled, so it may take a week or so to get the tank back filled, and mostly people just do a tank swap.