Just stumbled upon a new flight option:
Since you are looking for "regional" airline options it might not include only prop operators ... :
Despite being a so-called "LCC" Transavia (HV - part of KLM) just commenced serving Edinburgh - Rotterdam four times a week.
Rotterdam is just about 60 kms south of Amsterdam and both cities are very well connected by frequent train service.
So, that might be a viable option if schedules fit.
Transavia flies B737 (not the "Max", though
)
Flight schedule EDI-RTM :
monday 14.50 - 17.10
thursday 20.15 - 22.35
friday 20.35 - 22.55
sunday 13.15 - 15.35
Times are local (UK = GMT / The Netherlands = GMT+1)
I've no idea why OP would want to fly Transavia for the sake of it rather than easyJet or KLM. It's certainly not an 'exotic' airline by any means. I suppose trying out RTM airport might be of interest, however, and price may be good.