You can buy them from ATCC for either $359 (non-profit) or $459 (for profit).
http://www.atcc.org/Products/All/HTB-20.aspx
I would highly advise you to get cells from a reliable source such as ATCC. Cell line contamination has become a big problem. This includes both getting the wrong cells (especially HELA) and also mycoplasma and other bacteria and/or viral contamination. You might save a few dollars and then find out that you wasted your time doing experiments on the wrong cell type. Also, the better journals are starting to require that you verify the cell line and this could cost as much money as just paying for the cells. There is an excellent article on this issue in "The Scientist" this month: