Combat Medic Archive

Your best bet is always with placing your own harvesters. I did just fine with personal harvesters for the longest time before I upgraded to mediums.

Survey and find a good spot with good OQ and PE on the resources you need and set as many harvesters as you can on it. Stockpile the best advanced resources you can.

If you pay someone else for the resources you will be paying from 10 to 15cr each for the best quality. WAY more productive to do it yourself.