The Birch Hotel in Haywards Heath is closer than Brighton or Crawley - approx. 10 mins drive from Burgess Hill if you don't want to trek to/from Brighton. Its an OK place (a Best Western franchise hotel) but it isn't as cheap as premier inn style places.
Having said that, as others have said going to Brighton will give you a much better set of options - and Burgess Hill is only 5 mins from the A23 by car so Brighton is very accessible.
Paul.