If it's too much for you then you should just rent a manual and should have considered booking a car months ago not wait till the last possible minute. Prices tend to go up during high season and guess what it's high season in Greece.
420 euro a day? What kind of car was it?
One final question was this to ask for advice or just a rant post?
https://www.amazon.com/gp/product/B076SDM2BQ/ref=ppx_yo_dt_b_asin_title_o07_s01?ie=UTF8&th=1
I have this and it’s worked well. The default cord that comes with it should with in Greece without the need for one for the adapter blocks that comes with it.