As far as the pricing model, what you say makes sense for larger companies. I'm thinking of small companies, say 10-20 people. Big enough that they do have some purchasing pain, but not $2k/month worth of it. Setting a low price point for them might get growing companies on board early, becoming larger clients as they grew.

For non-SaaS, I didn't have anything specific in mind. I know that my teams have purchased, at various times, IDE licenses, "Pro" versions of various libraries and tool, and even licenses to run various servers that aren't free/open source. The catch in my mind is that if "procurement-as-a-service" covers all my bases, it may make sense. But if I need an internal procurement person anyway, the value prop of your service diminishes a bit.

I like the idea overall. I'm a believer in hiring for the core product, and outsourcing the rest, and this idea fits in nicely with that philosophy.