Adding oxygen to wort/ yeast starter

Hi, had some other questions occur to me. I was thinking of buying an oxynator kit, but they seem awfully expensive at 35-45 dollars. Can someone suggest a cheaper alternative? are the regulators and stones available elswhere for less? would using a medical oxygen tank and a hose and stone be better?

If I have extra malt extract, can i boil it in a little water and add yeast? or does it need to be hopped as well?

Thanks!

John