Been a few times as the inlaws live just outside of Budapest. Its a good weekend, one of the better tracks for spectators I believe. Cant advise on accommodation as I just stop at the inlaws but like everywhere the prices will be bumped up for that weekend. Theres free public transport on from the city centre to and from the track. Budapest is a great city anyway and is still very cheap for food and drink.
Also, flights into Budapest are expensive for that weekend so look at flying into Bratislava as the flights there with Ryanair are cheap as chips then its 10quid each way on the train to Budapest (takes about 90 mins)
Either way, please take a dummy, a teddy and a blanky for Lewis Hamilton as he will probably thrown his toys out of his pram at either of those Grand Prix too.