You are correct that the cost of the 6300F is more than the 2930F but also keep in mind that the 6300 series is inline with the 3810 switches. Although you are looking at the 6300F model feature wise it is still more in line with the 3810 even though it is the fixed version and not modular.
As for which one to go with all depends on your needs and preference. If you already have some Aruba switches then you might want to keep the OS type the same but if this is a new install alltogether then I'd weigh the differences and see if the price increase is worth it.
The 6300F will give you the NAE which is very powerful so if this is something you would use then I'd seriously look at this. The 6300F also gives you SFP56 uplinks to allow you to go 25G uplinks or 50G VSF stacking.
They both will integrate with ClearPass so I wouldn't worry about that portion of it.
The 2930F has 90 days of 24x7 phone support and 8x5 phone support for the life of the product while the 6300F has 90 days fo 8x5 phone support and then you would have to purchase support after the 90 days. If you require 24x7 support you would have to uplift to that for both products.
If you are looking at using Aruba Central to manage the switches the 2930F is supported in Central today while the 6300F isn't so take that into consideration as well.
Hope this helps and good luck on your decision. You can't go wrong with either one.