I just wanted to suggest a 3-tier system by which Ring of Flying grants flying and is lvl 1, Eagle Wings grant flying and are lvl 2 and Atavian wings grant flying, Eagle wings and the extra exits and are lvl 3.
Considering the credit prices of these three artefacts (400/800/2000) they are normal for a 3-tier system except for the Atavian wings' cost progression. The reason I think the 3-tier combination would work is because it's kinda weird how the Eagle Wings and Atavian Wings can fly so high but can't take the user flying. The implementation of the three items as 3-tier would allow people to progress from one from the others, which as I recall is already done Eagle Wings to Atavian Wings but probably wouldn't hurt as 3-tier.
Thank you for reading my Idea.