There is a special item requirement - The gold is just hand waving for the item requirement.
DNDBeyond says:
"For each level of the spell, the process takes 2 hours and costs 50 gp. The cost represents material components you expend as you experiment with the spell to master it, as well as the fine inks you need to record it. Once you have spent this time and money, you can prepare the spell just like your other spells."
Being in the middle of no where with a spellbook, scroll, and gold will not help you scribe that spell. You need to spend the gold somewhere to buy inks and components...
They should add an "arcane ink" item add for inscribing that each unit is worth 50pg. Then add some vendors and add it as loot as well...
Attach that to happen in camp only, there you solve the problem (makes sense only use gold there considering all the staff in camp that you could buy this from) and have another reason to trip back to camp XD
