Which NGC Grading Service Level To Use?

I have some coins I plan to send to NGC (I'm a member), but I'm not sure if I should use the $18 Economy or $30 Early Bird pricing level. (I'm sending in at least five so I could use the $18 Economy category.)

I think the value of the coins is $300 or less, which would qualify for the $18 Economy, but there is a chance a couple of the coins might be graded at a level which would put their value at more than $300, which would mean I'd need to use the $30 Economy.

For example, I have a BU Barber that would be valued at $230 if it's an MS-63 (which I think it is), but should it be graded MS-64 (and it may have a shot) its value would be $360.

How should I proceed? If the coin grades so that it's value is over $300, does NGC automatically charge me the higher cost? Or do they simply go on my estimated values on the coins.

I've only submitted one batch of coins to NGC, all at the $30 Early Bird category, so I'm not sure what's the correct thing to do.

Advice?