Originally Posted by BobFF68

Saudia uses Plusgrade to manage paid upgrades, if you have already an active booking you can bid the upgrade at SV website any time, the page will show you the minimum offer that is based on specific destination, regardless of time and seats availability for what I was able to see. For instance last April I placed a bid for the leg CGK-JED from Y to J (no F offered in this flight), minimum bid was 362 USD that was accepted 24 hours before flight. The other leg JED-MXP minimum bid was 272 USD but I did not place any as was only a 5 hours day flight.

I have a new trip already booked for year end holidays and the minimum bid is always the same as above, from my calculation considering the actual price for rebooking on J there is a saving of around 50% vs the minimum bid. For sure there is no 100% guarantee that space will be available or bid to be accepted at the level suitable for you. About upgrades at check in I have no idea and not sure anybody here will be able to answer you.