From the last 3 free ones i got 14 gems.

From all the free ones combined i got 169 gems, but i dont recall how many crates that were.

There is a tipping point, you need to have filled many of the crate draw items, then almost everything creates instant gems and/or you sell all lower end rewards.

You need to be prepared to spend about $200-$250 in order to fill all/most of the slots. Seems like at around $150 you start to see mostly gems.

Crates have 5 slots, 2 for Consumables, 1 for a blue or better item, 1 that can be anything, and a 5th bonus slot that is purple or better.

Consumables are always able to be converted, so you are looking at 2-3 gems per crate at the very least, so at the very most, you are looking at 40 crates for 100 gems, though that is assuming you are getting 50/50 on slot 4 and no slot 5's, along with no repeat drops.

However, based on the drop pool, and such, even if you were unlucky, you would get furnishing or scroll drops that could be converted, along with duplicates, so we can probably halve that number.

So if you were unlucky, I'd say 20 would be the max, but even then, you'd probably get pretty much everything in the lower tiers as well as some yellow and purple drops.

Assuming you are after a particular 100gem tier item, and you consider anything besides that item or a radiant apex mount bad luck, plus you have none of the items previously, I think 38-39 crates is the absolute maximum you would need to get.

Keep in mind, you would then have everything from blue up you could get for gems aside from scrolls. More likely, you'll get a number of blue diplicates for about 7-8 gems a crate before then. I think duplicates are more likely than not due to category weighting. This was rumored back when nixhound was the only pet in its tier and players kept getting it.

After 15 crates I gained 104 gems, extracting every possible consumable. I got the Flameback Boar x3 so the purple duplicates added quite a few gems.