sergeantmajor, this is exactly what DS (and DH who is an economist) told me. And for some careers it does matter where you go, in that some aspects of economic research are very mathematical and employers will know which Universities/courses cover the ground.
The good thing is that salaries afterwards can be very high indeed. It essentially becomes an investment decision. Without crunching numbers, it is almost certainly a good investment to pick LSE, say, over many RG Masters courses.
I would get your DS to speak to the LSE, and to Cambridge. They will have come across this before. As I said earlier, two of DS' very able friends came from first generation immigrant/working class families who almost certainly could not have afforded the fees out of income.
www.moneysavingexpert.com/students/postgraduate-loans/ is only slightly helpful. It appears that government Career Development Loans are no longer exist but that some financial institutions are willing to give personal loans. (Or at least several came up on Google.) This sort of Masters is much more akin to law conversion courses or similar. It will be a year (or two) of very intense study to gain technical skills. Or take a gap year. Interalia DS and several of his friends were able to find work as Research Assistants, DS over the summer, once their had completed their UG degrees. And there is plenty of tutoring work, especially for someone able to support first year econ students struggling with first year compulsory quantitative courses.
He needs to scrutinise courses carefully. The LSE Masters is quite mathematical (indeed a generation back, DH did not apply for this reason.) Cambridge used to offer two Masters, one in Econ Research and the other straight Economics. I will probably be flamed, and perhaps correctly, but the latter is considered less rigorous, and perhaps more the territory of those willing to pay to have Cambridge on their CV. The Oxford Masters is very well regarded but two years, and UCL and Warwick would be worth a look, as their UG degrees are very well regarded. My recollection, from DS' applications was that LSE considered applications as they came in, and so it was worth applying early before the course filled up.
He will not have much, if any, time for paid work.