The cost of repairs to our 2006 Vauxhall Astra is spiralling - what should we do?

Having saved diligently for a few years my 22 yr old son finally bought himself, last October, a ‘decent’ car (Astra Diesel Hatch 1.9 CDTi 16V Sri 3 door - 2005) for about £7000 from a reputable garage....