You say $60 or $70 per week is certainly no bargain when you can get a second-hand phone to *keep* for that kind of money and just buy a local prepaid account readily available in lots of local places.
Why buy second hand? I just made a quick check at one of the four Greek mobile operators and you can get a phone to keep plus some initial call time as follows:
(all prices in Euros): a)19,90 euros with 8 euros call time b)14,99 euros with 6 euros call time
You have a choice of the following phones: Alcatel O.T.153 Ericsson T290 LG L341i Motorola C155 NEC 331i Nokia 2650 Siemens A65
Time renewal comes in 7 and 15 euros.
Phones provided with prepaid accounts are usually blocked to the carrier for six months. On the other hand with similar prices you can get a second phone in Turkey and pay less than the rental or second hand prices mentioned by other readers.