Depending what you mean by round 6 (after 5th or 6th reset) the cost per spin is 2100 or 2450. Both are then in my acceptable range.

Ampies are probably worth getting, but not sure if clearing whole box to get them is good. Bloom dragons I assume are the best ones, and they are similar in how hard they are to get to 100 level manyus, so I am fine with spinning for them to like 3k per spin, so on 7th reset with 2800 cost they would be still worth spinning in my case.