I am buying just green shards and ocasionally ( I understood that not more than 5 times/month blue shards)
In rest market is provinding only craps items
You're probably not 6-starring champions consecutively, otherwise you would not write this. 2-star champions are the most valuable offer in the market aside from ancients. To demonstrate their value, a quick calculation.
Let's assume you have lvl30 and 40 food ready. To make one 4* chicken, you either level 3 green champs for 80 energy and then rank them with 6 more green champs; if you bought them it's 80 energy per 4* chicken. Or, if you have to make them from grey 1* champs you're doing 3 runs for 24 energy to get them to level 10 and rank; then spend 80 energy to get them to level 20; then do another 2 x 24 energy to make 6 lvl 10 grey champs and rank them. That's 152 energy compared to 80. Now, to get 5 5* chickens you need 20 4* chickens. Difference is 1600 energy vs. 3040 energy = 1440 energy or 11 refills or 440 gems. To this you can add the food you need to make lvl. 30 and 40 if you are not using rares.
And yes you can get 2* champions from green shards but 1. those are better used in summon events 2. if you're actively 6-starring champions you'll run out of them pretty quick. So, my advice is: refresh your market and buyout all green champions (and shards ofc), even if currently you're not leveling anything, it will save you a ton of resources in the future.
Also, considering the prices, you'd have to pay 1M+ silver for a 6* grey piece of gear.