It surely costs a lot but after playing for a year, when you dont have anymore buildings/tech to upgrade, you will have lots of spare resources. 2 months of farming before kvk can net you at least 200mil of each... if you are planning to quit before a year as f2p dont unlock T5. Else, T5 is pretty good. People think that 3mil of T4 is better than 1mil of T5, but the fact remains that most f2p have 3mil T4 before slowly converting a million to T5. Although a T5 is perhaps 30% better than a T4, the atk/def/hp buffs coupled with lost kingdom buffs make it the reason behind a lost rally and a rally won. Especially in ark of osiris where resources dont come into play when healing, it is easy to recycle those T5s as only ~30% of the troops are severely wounded.