I think the $120 a month extra would give you a Direct line for support from the "Core Team" but I would also read that the difference is that they are looking for some Support also for the project (which is not illogical).

Possibly the rates for different Server Runs are different as well but you would need to explore that I expect.

Sorry for the late reply. To clarify, the business plan is exactly the same as the budget plan with regards to the Hub and AWS feature set, with the exception of included premium priority support. Below is an excerpt from the detailed explanation you get when clicking on "support" in the plans page:

Premium priority support

Priority support is for companies that want to know they have a reliable commercial
venue they can turn to in case they need timely assistance.

The service includes:

E-mail and phone assistance: for up to 2 support incidents per month on issues 
limited to the TurnKey runtime and default application integration.

If during the support process the issue is determined to be a bug in the appliance
a support incident will not be counted.

Note that we can't commit to being able to help you configure a TurnKey solution
to meet your needs or support any special user-specific customizations, though
we will try to help when we can on a friendly basis.

Emergency response: notification of any critical security issues that require 
immediate intervention and assistance in fixing them.

To clarify explicitly - reserved instances are supported in exactly the same way in the business plan as they are supported in the budget plan (maybe we should tweak the wording / UI for clarity). It is up to you to decide when you want to reserve an instance, for what duration and at what size, etc.

I hope the above helps. If something still isn't clear, please let me know.