Be blunt with the company, negotiate something better, or join later, after the raise, if you really like them.

If they can only pay this price, they should get a junior intern, not an employee. I don't know which incubator they went through, but no mentor I know would have told them this is a good offer to give to a developer. 1.4k a month is what you'd give to your best friend helping you with your startup because you can't afford more, not your #1 employee.

I can totally imagine how it feels like on the other side, and it's hard, and they probably do a lot of very nice things, and may be very nice people, but giving such a low salary is not a good move, and they should know it.

I didn't mention equity so far, because, well, as @MehdiEG said, it's only icing on the cake, nothing more.

Good luck!