Sowing Rates for Borage, Catnip, Chamomile, Lemon Balm

I am interested in purchasing Borage, Lemon Balm, Catnip, Chamomile seeds. I need to know: A) How much of each type seed would I need for 1/2 acre plantings? B) Is there a better price rate on this sort quantity?

The seeding rates for sowing directly into the field are as follows:
* Borage 1.5 kilogram per half acre,
* Lemon balm 2 kilogram per half acre,
* Catnip 3 kilogram per half acre,
* German chamomile 1 kilogram per half acre.
Richters price structure has a built in discount for bulk seed. Kilogram quantities are relatively cheaper than 100 gram quantities and cheaper still than 10 gram quantities.
Large orders of $2,000 or more (Canadian funds) are eligible for volume discounts.