If the channels are fta & if you have sky digibox then nothing if you can find a 60 or 80cm dish kicking around (check skips and roadside bins!). as long as the lnb is a wideband or digital lnb then point the dish at the satellite with the channels you want. run the cable to your digibox and swap the cables over (or buy a coax switchbox). Find those chanels using "add channels" in your menu refering to such publications as "what satellite". The channels will stored in the digibox (I think limited though to 20 or 40 forget which).
Other than that a new satellite receiver, dish, cam & card or patched receiver - can be pricey using the second method!
If you are referring to the Greek channels on Hellasat at 39 degrees east, then a $ky digibox won't owrk for most of them.
The satellite channel details are here : http://www.lyngsat.com/hellas2.html
But the $kybox will only lock to symbol rates of 27,500 and 22,000 - which rules out most of these.
A £50 FTA (Free To Air) box will get these though using an old Sky dish and (universal) LNB as mentioned above.