On my server greens are around 10g and reds usually fetch about 20g.
I'd also like to find a good way to atleast procure base slivers and shard so I can upgrade my mount.
for 4-6 base, i have yet to find a good way of obtaining it.
im too lazy to get another class past 20. hopefully someone else would run the numbers.
the best choice of obtaining it at the moment is through supply box daily. but it is only once a day.
as for 7-10, AH is the best choice at the moment, it is dirt cheap @ 1g~ for green. not too sure what to do about red.