Using Booking.com is a quick and easy way to find what is available for your dates (you can sort by lowest price first). There are currently many options available for under £70 per night in small hotels and B&Bs near the venue. But be aware that not all hotels are listed on Booking.Com, Premier Inn for example, are not.
There are many B&Bs in Brighton, most very close to the venue. You will find a comprehensive list here: www.visitbrighton.com/accommodation/bed-and-breakfasts
Experience Freedom - the nearest campsite - is 2 miles from the venue, and is connected by a public bus route.
They have tent pitches, camping and glamping pods, and airstream motorhomes. Touring pitches are available on the adjacent site.
The Homestay website offers rooms in private houses in Brighton.
The AirBnB website offers apartments/houses/rooms available to rent.
The Visit Brighton website has information and a search tool if you are looking for accessible accommodation in Brighton. There is also more information about accessibility in the area on their other webpages.