Ever since Aegean expanded the "business basic" option to basically the entire network, it's become basically impossible to get 5k with less than 375€. The cheapest international A fares are around the 150€ mark, but these now only deliver 2200 instead of 2500 and if you add 40€ per leg for the new "full" business class fare, then you exceed the 375€ mark.
However the price of 37,50€/500miles is only valid until the end of Mai, so you need to start planning and purchase any additional miles needed by then, in order to avoid paying more.
You could for example fly WAW-ATH-WAW on June 5th in Flex T and back on the 8th in A. In between the two segments you could fly ATH-SOF in A, either with a direct return on the 6th, or outbound on the 6th and inbound on the morning of the 8th for +33€ (if accommodation is cheaper in SOF it could be worth it).
All in all 4 segments and 7346 miles for under 600€ (584,99€).
But I will ask the question: Is it worth it? I mean you 're looking at nearly 800€ (including the cost of the rest of the miles you'd need to purchase) us whatever the hotels and trips to/from the airports will cost you, so probably close to 1000€ plus your time, just to retain gold next year, when you will be taking (if all goes well) a number of flights, including long haul flights and of course the 4 A3 segments, isn't it worth it to drop to silver this time, reach gold again with your flights next season and use some of the 1000€ you won't need to spend now to make next season's travel more comfortable (and to make up for the lack of gold)?

PS. You could replace WAW-ATH-WAW with WAW-ATH-HER-ATH-WAW in Comfort Flex S for 331€ (just +57€) and 4600 miles (instead of 2946), which could save you a few €€, even more if you could find a discount code that's working for you, but I doubt the cost can get much lower than than in this time frame.