Virginia Caye, which lies five miles off mainland Belize and takes about 30 minutes to reach by boat, comes with a one-bed wooden house, a timber cabin on the beach and a boat jetty. It also boasts a coral reef and is perfect for snorkelling, dolphin spotting and bird watching.
Miss Reed, 40, has spent £100,000 on improvements, including a water collection system and solar power, with a back-up generator for the rare times the sun is not out.
But she has reluctantly decided to sell Virginia Caye because she does not use it as often as she would like after starting a business in Bristol.
She bought the island while she was grieving for her mother Virginia, who died from cancer at 68 and after whom the island is now named. "I went to Belize about four years ago and I just fell in love with the place," she said.
"At the time I had been building up a pub in Taunton and then my mum died. I just wanted to get away and do something interesting.
"I found an island and I decided to buy it. I got a loan from the bank and used money from the sale of my mum's house. I went out there to mourn my mum really and now I'm back in the UK and life goes on in a different direction." She added: "There were three battered buildings on the island so I had to strengthen them up, put in a walkway, get water tanks and electrics fitted.
"But in the end I realised it would need millions to really transform it.
"It has so much potential and for the right person it could be a wonderful escape or a great investment opportunity. It would really suit people who want to see if they can be self-sustaining or I could see it being an eco-tourism retreat." She has given the lot a starting bid of £400,000 on eBay but it comes with a 'buy it now' price of £750,000.
Belize has more than 200 cayes - sandy isles on a bed of coral - as well as the longest barrier reef in the northern hemisphere at 200 miles. Its reef and islands were declared a UNESCO World Heritage Site in 1996.
Miss Reed said the island generally enjoys summer all year round, although hurricanes are possible from August to October.