Micra NATS unit issue

[nissanmicraxs]

Hi guys

Newbie here and first time poster so I apologise if my post goes against any forum etiquette in advance.

I have a Nissan Micra XS (2004, 1.2L) and two weeks ago, I got into it and it just wouldn't start. It seemed like a dead battery but two different friends' cars tried to jump start it and nothing. Checked the wiring and a few other bits and bobs and all seemed fine so got it taken to my local garage. They said it sounded like an ignition key issue but once they looked at it, they realised it was the immobilizer/NATS unit. 

They've looked at it for a full week now, tried putting a new part in and still nothing, it just won't start and if they do get it to start in one instance, it reverts back to not starting the next time. The garage just told me this morning it seems like more diagnostic work is needed on the NATs unit to figure out exactly what the issue is - and unfortunately, all his mobile technician contacts won't touch my car given the issue. They said it sounds 'too much of a headache' to diagnose. So they're recommending the dealership - whose prices can obviously be hugely different from the guys my garage knows. I'm really confused about what to do, I've been reading online and read these electrical issues can rack up hundreds... my car is only worth £1500. Is it worth taking to a dealership? 

I've never had issues with my car like this, this is my first ever car so truthfully, I have very little experience with this kind of thing - I would be really grateful for any advice or insights anyone here could offer.

Thank you in advance!