At what point should our startup file for patents?

If you have technology to protect, and you want to protect it via patents, you need to file patent applications - even provisional patent applications - as soon as possible and certainly before you publicly disclose your technology in order to also protect your foreign patent protection if you foresee foreign patent protection. Provisional patent applications can effectively be done more inexpensively if they truly disclose your technology completely, accurately, and thoroughly because they will be used to provide a priority date for your later-filed non-provisional applications
which must be filed within one year of your provisional application filing date. If you want to protect your technology in foreign countries, you will also need to file a PCT application within the one-year period - you then will have, normally for most countries, 30 months from the provisional application filing date to select those countries within you want to file foreign patent applications based upon your US non-provisional and PCT applications.

Just to add that since your tech is still being developed, one strategy is to file multiple provisional applications (once the first one is drafted, subsequent applications should be more affordable) to keep up with important improvements to the invention.
Upon filing of the non provisional application you may be able to claim priority to one or multiple provisional applications filed. Which priority or priorities to claim will depend on your particular situation.

First to answer your question, yes! you should file a patent application, preferably provisional patent application since your product is being developed and come out within a couple of months. In order to save initial filing cost, as I said, you can choose to file the provisional application. Please mind that the provisional specification should also be same care as that of a non-provisional specification. You may also consider outsourcing the patent drafting services to save cost.

you can always seek an experienced patent agent for the subsequent strategy of protecting the patent.

Hope it answers to your query.

Best Regards
Senthil