Are there services that offer to recover data from irreparably water-damaged iPhones? I have an iPhone 6 which took a dump in a river. Since then, it will not turn on and does not register when connected to a computer, i.e. it is dead for all intents and purposes.

Does anyone know of a company that offers to read the data directly from the iPhone's flash storage or if this is even feasible (considering that damage is likely with the logic board since exchanging first the battery, then the Lightning connector and plugging into external power did not allow booting the device)?

I am aware that such services may be very costly. I was just wondering if there is a market for this kind of problem at all.
Yes, contact any major data recovery company, ex Drive Savers.

http://www.drivesaversdatarecovery.com/devices-supported/apple-iphone-data-recovery/