Ain't that bad imo, you have quite a solid amount of lower tiers already. Personally, I'm aiming for 15k/5k
It would take you 1 mil to upgrade bleachers and 1,4 mil to upgrade LT.
If you want a quick fix, I suggest simply adding 5k bleachers, you'll have a nice 15k/3k/500/20 arena. Not that far behind any team.
Or maybe you planned 13k/7k ultimately, I think it's the somewhat of a consensus best choice.
Or go for 10k/10k but I don't like it. For example, you're selling 10k bleachers at full price, so it wouldn't make sense to further decrease lower tier price, when you have opportunity to sell bleachers at 20
Maybe try 12k/8k, I don't know, but I think 10k/10k is overbuild