But for this one, my idea is more focused on affordability and drop variety rather than being the next best thing. How will I do this? Well, it's simple. Since price formula changes are very unlikely to happen, I decided to try targeting the next best thing: the stats.
I'm having sets be put between the Forsaken and the Cybo set tier-wise for two reasons: to give top-tiers a more affordable option and to make the current best sets more worthwhile as an upgrade. To do this, I modified the best offensive stats of each set tier from Paladin onward, with Lunatic as the base tier, in a way that each set piece will feel more worthwhile of an upgrade than the one before offensively. Take a look at this excel spreadsheet, first with current set tier boosts:

As you can see, the set bonuses are low as time went by, especially with Warriors, Whipmasters, and Gunmen. This is something I personally think holds armors back. Now, let's add in my in-betweeners and modify the stats to be more ideal:

Should my suggested in-betweeners be added into the game and the stats be modified to where each tier would feel more worthwhile than the last (at least +10% rounded for each offensive stat boost per tier), we're looking at offensive stat boosts for the current top-tier sets (Cybo, Crescent, Crow, Saw, and Parasite) going up from their fairly lousy boosts to around +23-25 in their best offensive stats, showing that the in-betweeners I'm suggesting here are essential for boosting the power of the current top-tier sets. The in-betweeners themselves would provide offensive stat boosts ranging from 19 to 22, which the current top-tier sets would be getting should the in-betweeners NOT be included. Therefore, it is recommended that my suggested in-betweeners be included.
As for the in-betweeners themselves, this would be the Defense stats for each.:
Warrior In-Betweener: 171
Wizard In-Betweener: 149
Archer In-Betweener: 149
Gunman In-Betweener: 153
Whipmaster In-Betweener: 166
So yeah, there you have it.