Depending on your model (you don't say) it is usually cheaper to replace the printer than to purchase a replacement printhead, if you can find one that is.
Are you aware that there is a possibility that your printer may be replaced by H.P. due to it having a printhead failure?
Here is a link that describes the condition where it may be replaced.
This is a link to an embedded link in the page above which allows you to see if you qualify for a replacement.