How much money do I need when applying for a Greek visa?

You don't indicate your Country of Residence, or Passport, but for an example, I used the Hellenic Republic (Greece in the UK) website.

If you look at the page I linked, under the paragraph Required Documents, is the following information:

• Supporting documents that clearly provide evidence of the following:

1. Purpose of the intended journey (i.e. confirmation of flight/ferry bookings etc)
2. Proof of accommodation (hotel bookings, original invitation letter dully signed by the host, whose signature needs to be verified by a Greek authority (police, honorary consulate etc). When the data regarding the host has not been verified by the authorities of the Member State dealing with the application, the applicant needs to present: A copy of ID card or bio data page of the host's passport; residence permit; proof of residence (property title deeds, rental agreements etc, proof of income).
3. Proof of sufficient means of subsistence both for the duration of the intended stay and for the return to the UK (i.e. bank statements, minimum amount for the last three months (please note that the minimum amount of money you need to have for each day that you stay to Greece is 50 euros, credit card(s) account statement, travelers’ cheques, salary slips, registered proof of sponsorship and/or private accommodation).
4. Proof of employment (this may be proved by a recent original certificate of employment/ pay slips/proof of social security contribution or for self employed applicants, an original letter from their accountant or the last tax return form ).

As you can read in paragraph 3, Greece wants to see proof you have sufficient means of subsistence both for the duration of stay as well as your return to your home country. They go on to indicate a minimum amount of 50 euros per day. This PLUS your return ticket home.

You would also need to provide the evidence required for paragraphs 1, 2 and 4 as well.

There's no fixed amount, and visa applications are all situational, but I'd recommend working out an itinerary and what you expect to pay

For 10 days, I'd have said €1000 would be plenty, assuming your flights are paid, but they may want you to have enough to pay for a hotel if, for example, you fell out with your friend and couldn't stay there.

Yes its true , I applied from kuwait,they also refuse many Visas here too. I got rejected twice too and the two people in fornt of me in the visa line. Here is the five most important things I learned the hard way :- 1- if you are going from another country not your current residence; you need to provide these tickets as well (2 tickts 2 ways,or 4 tckts one way). 2- you need to complete at least 3 months in the current residence country and same bank also. 3- exact days(Numbers) in flight tickets must be same in hotel even if your day is switching at 12 am\pm book the extra unneeded unused one. 4- Always book the refundable flight tickets\hotel. Best of luck. 5-Leave additional amount of money other than regular salary = Number or days x 50 euros. best of Luck