Should the invention be made open source if patent is not affordable or patent the invention? Which is the best approach ?

Yes, if you can't afford costs for preparing, filing and - eventually - prosecuting a patent application for your invention, or don't want to protect your invention for any other reason, you should consider "to make it available to the public by means of a (written) description" such that it forms part of the state of the art.
If you don't "publish" the invention, a third party making the invention (independently) and obtaining a patent at a later time could stop you from practicing the / your invention!
There are different ways to publish the invention. Some prefer publications that are generally difficult to find, but can be relied on in case a third party tries to stop them from practicing the invention.

We suggest to find someone who might is interested in investing some funds to invention. If it can patentable and have market scope. Someone might be interested.
We can help you identifying an interested person or entity.

Rucapillan IP is a leading patent commercialization & management firm. Contact us at ramandeep.singh@rucapillanip.com or visit www.rucapillanip.com