Me and the brother in law did it in 2019, we rode down to Liverpool for the ferry. £395 return each for the rider and the bike, on the Island we booked a Bell tent on the football pitch at Castletown, I'm sure it was £50 per night each for the tent and bedding and a towel, they did quite cheap breakfasts and evening meals and opened the bar for drinks in the evening. There was showers and toilets to use on site. It was a 10 mile trek up to Douglas for the racing but we were later in booking so it worked for us. Hope that helps a wee bit.