A main complaint against allowing players to buy lower-level boxes was that they would farm at level 30 in PvE and use the higher price money to buy the boxes, giving them an advantage over the lower level players with less income.

Therefore I would suggest you can choose the level of the boxes you want to buy with two restrictions:

1. You can choose the box level (within restriction 2), but you have to pay the box-price according to your level
2. You cannot choose a box-level higher than your own level

This would mean that a Level-10 Player cannot buy a box higher than level 10, so he would not be able to get high level stuff cheaper (except for the already implemented 2-level-range). But he is free to buy lower levels. The latter part is meant for the Level 30 and other high ranked players. It would allow them to create mechs for lower level fights, but it would drain their larger income from PvE (PvP price money depends on the level of the fight, not the player) to prevent an advantage.

Overall I don't think this is too big of an issue.

voted plus 1 , hopefully the update shall happen.