Frist of all I want to say that I could subscribe for crafting bag and it is not that expencive. But I know myself better. I played WoW 3 months and I loved it and hated it but afterwards I mostly hated it. Becouse of the subscription feature I felt like I was wasting my money when I didn't play WoW, which in turn caused me to play as much as I could and it had a bad effect on my social life and school. I like ESO becouse I can use Crowns to buy every DLC with one time purchase and then play as much as I want when I actually have time to play and without worrying about paid game time running when I am having fun with my friends.
However, due to ZOS adding new motifs all the time, it is starting to become impossible to be a crafter without ESO+. Both my bank and bags of every character are mostly filled with crafting materials. The bug that gave me ESO+ for 2 days was a blessing as it opened 171 slots in my bank, 41 bag slots on my main character, and 152 slots on my "main mule". I could finally experiments with some of the sets I never had been able to use (Ice furnace, winterborn, Spellweave, Rattlecage), but this of course is coming back to me soon. Since I now have collected a few cool armor sets and a couple of the new monster sets, I no longer have space for materials when I get to that point. Now that housing is coming I also need space for furniture materials and the furniture themselves, meaning I will have to get rid of most of the sets I have collected and a few other items to make room for the housing stuff.
Hence, I suggest adding a limited access crafting bag in Crown Store. If I was to introduce it I would create it as follows:
Crafting bag: 3000 Crowns - Unlocks 20 slots on your crafting bag, can be upgraded for more. (~ 21€)
Crafting bag Upgrade: 1000 Crowns - Unlock 10 extra slots on your crafting bag. (~7€)
For comparison: ESO+ - unlimited access to crafting bag for the duration of subscription (~13€/month [or 15$/month]), in addition to other perks.