@PettsWoodParadise if I'm staying in Cambridge, I go cheap and cheerful at Orchard Park. We normally stay in the Premier Inn but if that's full, Travelodge is ok. For DD's MA upgrade graduation last year, we spent just over £100 for 3 nights in the Premier Inn. Parking is free and undercover. As DH said, what we save on the hotel, we can spend on taxis, and even with them it was less than £20. We do use the bus or drive to a park and ride. When DD lived in college, it was an 11 minute drive. Now it's 8.
@Panicmode1 you'll have to PM me with where you are based. In all the time driving to Cambridge from Devon, I found the best time to do the A303 is leaving at 6am so you pass Stonehenge at 7:30 - 8. It's fine on a Saturday or Sunday morning. We've also gone M5, M42, M6, A14 which sounds bizarre but isn't much further. If the weather forecast is dodgy as it was in DD's 1st year where we had snow flurries in Cambridge, it's less likely to be problematic.
@PettsWoodParadise taking the train costs triple the amount of fuel and there are no convenient stations round here. I'd have to go through London too. My dad wouldn't be able to cope - he just about managed with his blue badge and me driving him to the door. The thought of lugging that bloody framed degree certificate on a train does not fill me with joy. DH has promised/threatened to fly us there as he has a PPL and access to a club aircraft. However, routing around some very busy airspace (Bristol, Heathrow, Luton) is an other issue. Car it is!