My DDs certainly do not live frugally at University - I wish!
However, it is possible and plenty do. The main thing is to choose the best university for his future career but, in general, ones in northern England have cheaper halls available and 2nd and 3rd year private rented accommodation available.
Do not, if you can possibly avoid it, start out in a flat share in the first year - regardless of the above advice. Most universities make this the default position for people who apply late and cannot get into halls. Not being in a hall could mean your DS will be a BillynoMates and have to work really hard at making friends. Halls are where almost everyone want to be, hence the over-subscription at some universities. They are fun, have organised getting to know you sessions, and are a place to make friends. Yes, there will be the odd very annoying person, but in general people will include your DS in going out, nights in to watch a film on the TV and generally have a laugh together.
I actually think catered halls are best because the new student has enough to think about getting used to academic and university life without the worry of organising food shopping and meals (and all the arguments about who used up all the milk and didn't do the washing up). However, this costs more but can have huge advantages for someone who likes to make friends and it is quite an easy transition from home. Shared rooms, if available, are cheaper and older halls are cheaper with shared bathrooms. New shiny ones are to be avoided.
He can try and get a job. This is not as easy as some people think in some university cities - everyone wants one. Also, you do not want a job to take precious time away from his studies. Also, he should not keep coming home all the time. This costs money.
The main thing is, go to Student Finance England and put in your finance details and get a quote from their on-line facility. Also, do not let him apply to London, St Andrews or Bristol as they are expensive student cities for years 2 and 3 when halls are not available. Can any grandparents help with a bit of money?