The reason a vendor can fleece public services in the first place is, somewhat ironically, the limited access to free public records by independent journalists. I’d reckon we need more freedom of information, more regulatory oversight, and more participation by the public. The cynicism that governments are inherently dishonest and feckless (rather than being designed as-such by the self-interested lobbies pushing this cynicism) is one big reason such corruption has become so prevalent.
I've always thought the reason a vendor can fleece the public is a mixture of 2 things.
1) You get elected by convincing voters to vote for you. Which is not the same as actually getting the lowest prices.
2) Core competency has been stamped out of a lot of government agencies and so if you're a skill negotiator you want to be collecting the commission from the sales contract to the government as opposed to a low salary from being the government agent.
So at the end of the day, making all these contracts public wouldn't fix future ones from being issued. Although I'm still for more sunshine.