It depends on the value you get. Some SaaS are free or cheap, they probably cost little to the company, or the company is running cheap (single founder in ramen).
Now for how much a single person spends, it's a different story. Let's assume your target audience is software developers. An average software developer should net more than $5,000 a month. Spending $150, is like 3% of his salary. Not a lot, so he could even subscribe to more services and more expensive services.
If your target audience is Egypt for example, where the developer net $200-$250/month, subscribing to only one service may cost 10% of his salary. So it's a luxury he can't afford.
Bottom of the line, your target audience and market readiness is the one that decide the price tag for your SaaS.
Now for how much a single person spends, it's a different story. Let's assume your target audience is software developers. An average software developer should net more than $5,000 a month. Spending $150, is like 3% of his salary. Not a lot, so he could even subscribe to more services and more expensive services.
If your target audience is Egypt for example, where the developer net $200-$250/month, subscribing to only one service may cost 10% of his salary. So it's a luxury he can't afford.
Bottom of the line, your target audience and market readiness is the one that decide the price tag for your SaaS.