If you buy silver nuggets for 3k, or silver sand for 2.5k the resale of Silver Javelin Heads breaks out slightly under even after HQ's assuming you make the majority of your synths.

But that doesn't include shard cost (12 wind 9 fire). If you look at that its around 3k gil per synth loss after all said and done.

You do these from 40 to 50, and my estimate on shard usage for that entire stretch is about 30,000 of each, or roughly 8 million loss.

Again if you farm the ores yourself, you save the cost mats + gain money from resale. That 8m will turn into ~3m loss if you go that route and again that cost can even be brought down by trading shards or desynthing the crystals yourself.

Then again, farming up cash in this game is ridiculously easy (150k per day from leves or so if you hunt out good ones) so you might just consider buying if you don't want to take the time to mine... at how fast most ppl craft you'll probably break even doing leves and spending daily leve money on mats.