For Greece, most nationalities do not need a visa. One notable exception is South Africa, where you must apply in advance. If you at all in doubt, pls check with your local Greek embassy. Most non-EU residents get an automatic 3 month visa-on-entry.
Turkey – most nationalities do need a visa, but it is a very simple online process. The cost varies according which nationality you are, usually from around 15 euros to sometimes up to 50 euros. The most common is around 20 euros.
Please note, your passport must be valid for 6 months AFTER your overseas travel is completed.