HP Cartridge cost , Pricing and ink levels

I have an HP All-in-one C3188. Its proved to be a worthy buy and i have used it quite a bit. My cartridge's ink seems to be very low now. First thing, i wasn't able to make out the current ink level on the cartridge. On right clicking the HP Printer icon, on the "Printing Preferences" menu, on the features tab, i can see a "Printer Services" button. This button doesn't work when i click on it. Well anyways, i decided to buy a new cartridge. There were 2 options, buy a new one or refill the older oner. I guess the latter is the unofficial way of doing it. I enquired at the BDA complex in Koramangala. There are 4-5 stationary shops there and one of them refilled Black cartridges at Rs125/- and coloured ones at Rs 300/-. As i walked way after the enquiry, he called out for me and said, he would refill both at Rs 350/-. The enquiry for a new cartridge numbers 851 (Apparently i was enquiring for the wrong number, i should have been asking for the number 850 which is compatible with the C3188) was surprising. I got 5 different prices from 5 different shops within the same BDA complex building. Prices varied from Rs 740 to Rs 825. I of course ended up buying the Rs 740 one and then later realized that it was not the correct cartridge. I ended up buying the correct one for 675/- only to later realize that the HP website was offering one for about 8-10 rupees lesser. I'm sure if i'd gone through the entire procedure of finding prices again, i would have got a better deal. This reminded me of the lecture by Dr Preston of Yahoo which i attended at the Leela Palace, Bangalore some months back. A very insightful talk about pricing.