The cost of a premium plus account is approximately double the cost of a premium account. Heck I'd settle for a 'premium plus, and I paid the difference between that and 2 premium accounts' option. Easier when setting up permissions, environments, etc.
*Correction* I went and looked, I'm paying $249/year for my premium plus and only $99/year for my premium accounts. Even more reason to give us the option at premium plus to use all of our tier for 2 Belli homes.