That totally depends where your location is . If stage 1 still takes place at Novotel in Southampton you can check in at Novotel , Ibis or Ibis Budget ; its a compound exactly where stage 1 takes place
If your stage 1 is at CTC in Whitely Fareham , the cheapest is The Premier Inn . Its a 45 min walk to CTC or 15 mins drive with cab . Hope this helps
And please for further NATS recruitement process questions read the massive thread . It really helps .