Proprietary software costs money and and free open source software costs time. Projects based on open source software often cost the same up front compared to competitive proprietary software. Your open source savings start when you do not have to pay heaps of money to renew a licence.
Your initial costs are mostly people time. Your staff need training. A good training course costs the same for both open source and competitive proprietary products. The implementation costs are greater than the software costs and well developed proprietary software used to have an advantage over open source software because the software had a better range of features out of the box. Today the top open source projects have comparable features and people with useful experience on the projects are easy to find.
The reason so many proprietary products are competitive up front is the competition from open source. The proprietary vendors have to keep the selling price down then rip you off on consulting, upgrades, and licence renewal after you are locked in to the proprietary product.
The reason so many open source proposals fail in the commercial world is the relatively recent maturity of the projects. The most useful project is Apache and no one in Information Technology would use anything else for a Web server if they were not locked into something else, usually Microsoft's IIS, by a non IT management decision. When you talk with management about the Web server software, you can point out that almost everyone else is using Apache of the few using IIS, quite a few were hacked. Few other open source projects have the maturity of Apache.
There are several open source projects that were painful a few years ago and a brilliant now. When you propose those products to prospects, the prospects ask their friends and their friends say
we tried that and it was horrible. The friends rarely tell the full truth which is often
we tried that many years ago, it had some problems, the Microsoft/Oracle equivalent had some problems, so we went with the brand name because we had a lot of money in the budget back then and could pay the vendor to fix the problems caused by the vendor.
Drupal is an example of a free open source project that went from unknown to known almost overnight when the White House chose Drupal. The White House is one of the few organisations everyone has heard of and lots of people who know nothing about Drupal or about Content Management Systems are mentioning the White House decision in news articles. Who cares about all the bigger projects using Drupal long before the White House. Few people have heard of the previous big successes. When you are introducing Drupal, you can start by saying
as used by the White House.
Here is useful software, based on my experience and the recommendations of other successful experienced people, plus the main competition that may be useful in specific circumstances.