cheap flights from Riyadh

apparently, Nas Air supposed to be pretty reasonable...

Try using the websites Momondo and Skyscanner

There are several cheap flights but it depends on how good at planning you are. NAS Air as previously mentioned and FlyDaubi if you book now for July you can get flights for around 900SAR return to Daubi. Others are a similar price.

SAR 900 works out to be £150, bit off a rip considering the flight time is only circa 1hr45mins. Internals here in the UK are cheaper then that, and fuel price if pretty hefty here.

Supply and demand they go up to 1000 SAR each way if you book late.

If you are planning to fly from KSA, you get the best options from FLYNAS.
However, go to expedia.com for the best fares to the worldwide cheapest flight fares !!

I like farecompare.com the best.  You have to chose three additional sites on farecompare, but farecompare is best.  Be sure to choose 'flexible' if at all possible (a day or two can mean hundreds of dollars difference!).

if you are looking cheap flights you can use travelfox.com/flights is a travel search system where you can search and compare thousands of travel web sites for the best deals airline tickets in just very few mouse clicks.

Thé app Jetcost is very good

kayak is goo too

NASAIR AND AIR ARABIA are the best... Also Flydubai.
Depends on the season that you go on.

From experience NASAIR is efficient, fast and less time for waiting and always on time.

NASAIR is equivalent to Ryanair.