Campaign experience impossible to earn as a level 7 mage?

I was looking at options for spending some time and money in downtime to earn a little extra experience and I noticed that it doesnt seem possible to break the gp threshold (2500) through conventional means as a 7th level mage.

Researching the most potent 4th level spells available to the 7th level mage costs 4000 gold and 2 months or 2000g per month.

Creating 4th level scrolls or potions costs 2000 gold and 1 month.

Neither of these options exceed the threshold of 2500g

Are precious materials the only option? Should the greatest return be scribing four 1st level scrolls per month. Each of them etched into a 10,000 -30,00 gold bar. To instead earn 38,500 - 118,500 experience per month.

It feels like there should be some middle ground between zero and massive. (If you can even spend precious materials on scrolls)

Or am I just missing something?

Technically, precious materials aren’t an option (ACKS page 118, emphasis mine):

For every 10,000gp of value in gems, jewelry, precious metals, and rare or elaborately carved woods added, the spellcaster receives a +1 bonus on his magic research throw. A character may not spend more on precious materials than the base cost of the item.

So on a 4th-level scroll costing 2,000gp you could spend at most another 2,000gp in precious materials, not nearly enough to get a +1 bonus…

On the other hand, there is nothing saying that you couldn’t spend less than enough gold to get a bonus—a scroll containing a first-level spell (like, say, sleep) costs 500gp to scribe and takes one week, but if you spend another 500gp of precious materials (probably monster vellum or gold ink) you can gain experience if you can succeed thrice in a month.

And here we get into the weeds of what is your rate of success, which is influenced by your level (7th, so base 10+ throw), INT bonus, ranks in Magical Engineering, workshop value (10,000gp if you have only just enough to scribe 4th-level spell scrolls), and whether you have a formula for the item (certainly yes after the first time you succeed at scribing a particular scroll, and it causes both the base cost and the base time to be halved, so it affects the XP you gain in the following attempts).

Now, I’d have to sit down and write a spreadsheet to compute which spell level would be better for experience gaining, but you’d probably be looking at most 1500 XP in a given month, if you succeeded at all your throws.