Buying grunil armor through the armor vendor is probably the cheapest way to get it, and more reliable than farming or trying to get one on the marketplace. Crafting one will run you over 300k.
It costs about 90-100k and about 12-18 energy per item. The vendor requires 500 amity and buying a piece will reduce your amity by 200.
So first you need to run over to Altinova . Here is a map from Heidel on the left to Altinova on the right.
The armor vendor is named Mevo. You will need knowledge of the merchants so you should go around the city and try to talk to everyone with a ?. Unfortunately you will need to talk to them in a specific order due to knowledge gating. Also Neruda does not sell anything so you can't just use the NPC buttons.
The best order I've found for everything excluding the dreaded "fail to interest" requirement is this. (the order in which you right click on them). This order is optimized for a higher success rate vs total amity gain. There is probably a higher amity gain order but it will be riskier.