You ultimately make money by doing every quest. I come out each day with an average pure sP earning of 3.5mil, 2 amulets (around 400k sP), 350 wiz tokens (1.7mil), 1 morty card (2.1mil) and 122 items.

This is my average earning per quest and total for all 15 quests for the day: This is using data over the last 100 days. Over those 100 days I only lost sP on Quentin three times. However I only lost 150,000 sP over those three days. I earned 160 amulets, which is 32,000,000 sP.

There's no reason to worry about the odd 2k sP loss per quest when ultimately you're making money in the long run.

Edit: And to make it a little easier to digest here's the forecast for a month using the average earnings I've made:

I used the very conservative average worth of 1000 sP per item given.

So if all goes well after four months you should be close to becoming a billionaire. That feels like enough sP to me.