Purchase requisitioning and management software

My company has a paper-based and error-prone purchase management system, and I'm wondering if anyone can recommend software to replace it.  We're an MSP, so we order equipment, parts, and software on behalf of our customers, then bill them to get reimbursed.  I'd like to find something that tracks 1) who bought something and when, for how much 2) who authorized the purchase, and 3) attaches receipts/invoices showing the total.

It's rare that we need to actually provide formal quotes--this is done verbally or via email, since most of our clients have been with us for 15+ years and are SMBs--so there's isn't really a need for pre-sales or CRM features per se.  We just want to simplify accountability for the stuff we buy for clients, so reconciling what we billed vs. what we should have billed is an easier process at the end of the month.  Quickbooks probably does some of this, but it's too complex--I'd like to find something lean and purpose-built for purchase tracking only.

Gotchas:  we cannot use a cloud-based solution.  This must be on-prem (we have clients with security agreements that prohibit the use of cloud services).  Also, anything over a few hundred dollars in cost is probably a non-starter.  i tried SpendMap, but the free, on-prem edition is so crippled it's basically useless (eg, requisitions module is completely disabled).

Any thoughts?