Kobold upfront cost rockets to Axeman level

Two kobolds cost 2.4x more than a sentinel, a sentinel attacking a kobold on plains has almost a 10x upfront cost advantage, with upkeep adding to the difference

Four kobolds cost 1.5x less than a marshal and retain a 13% advantage on cost defending against them on plains. Knights very likely have a cost advantage attacking them on plains at current prices, plus the large retraining rate advantage

Two sentinels cost 3.6x less than a marshal with a 50% advantage defending against them on plains. Kobolds retrain defence against cav on plains 50% faster, but it's not crazy to build sentinels for defence on plains against cav right now

Basically kobolds and sentinels used to be absolute cost stars, while with prices at the moment kobolds have no cost advantage. Sentinels lose some of their beastly cost advantage but keep it strong due to being a two upkeep unit that costs a beer and bow

Marshal vs kobolds

Four kobolds cost 2540g, marshal 3735g. Marsh kills 6.8 on plains for 3735 to 17,272 upfront cost difference at a 4.6 cost ratio  Upkeep is in the marshal's advantage, increasing the absolute difference over time. Holy mother

Marshal vs sentinels

Two sents cost 1080, marshal 3735. Marsh kills 4.8 on plains for 3735 to 2592. 1.44 upfront cost ratio for the sentinels. The 4.8 sents to match one marshal have 9.6 upkeep vs the kobold's 6.8. The kobold's relatively better upkeep vs the sents for defending on plains takes 218 days to come even at this price

While the marshal costs 40% more than 4.8 sentinels the upkeep difference brings them even in 9 days

Proper marshal vs kobold on plains, 3735g for the marshal, 4318g for the 6.8 kobolds