Where can you find cheap Doctor Who DVD sets?

well most that's I've seen are like $100 if you live in Australia (probably 50 pounds). in Australian stores you can get them at 'JB HI Fi', 'Myers', 'Sanity', Borders' and you can rent them at 'Video Easy' pretty cheap, and lots more stores. the only box sets I've seen are series 1, 2, 3, and 4. you can also by each episode singularly. at 'Video Easy' you get get the old series as well. but $100 is really expensive. you can get them allot cheaper on 'Ebay'.