A degree shows a level of attainment and a skill set. A prestigious university can help open doors that otherwise might be closed. As has already been mentioned, some companies will only consider top flight institutions because it's an easy screen of candidates. Also, while people don't like to talk about it much, having the same alma mater can make an interview go more smoothly (but then so can sharing any other interest). In the UK, there's not that much variance in price between Oxford/Cambridge and the lowest ranked universities, so there's not the same dilemma.
I've been hiring for over 15 years at various sized companies, and it's always been down to the skills demonstrated and not where the candidates got them. After your first few jobs, the university itself starts to become irrelevant. If you can prove you have the skills then you'll get hired.
IMO - you've already got experience - go for the cheaper option, carry on getting more experience on the side. If you need/want prestige later then get it through a masters when you have the salary to support it.
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