Well while you are considering things........

A Homefill II / EX2000 by manufacturers specifications requires an input of 0-2 lpm, at 14 - 21 psig.

Using those figures you "should" be able to use two compressors for a single 5 lpm oxy con or four compressors from a 10 lpm oxy con. 5 lpm oxy cons usually have on output pressure around 10 psi, 10 lpm oxy cons are usually 15 - 20 psi. So theoretically you could run 4 compressors off of one good oxy con.

Also these Homefill units can easily be garnered for $500.00 or less used. The man I got mine from had the compressor and an oxy con for $500.00. He alos stated he could duplicate the setup for that price by the next day.......
These units require a medical license to sell and a prescription to buy. Unless you get them used, there is not a great demand for these units and sellers often get frustrated. Ebay does not allow used oxy cons to be sold. It can be difficult to find a buyer given the circumstances.