Free if you collect from Edinburgh area. I have more photos and more details which I can share.
I have a set of bed rails from a vintage (circa 1960s) bed, they have been extended to be 7 feet long. You will need to find a headboard and a footboard (antique and vintage furniture stores or house clearance dealers). You bolt them to these rails and you create a 7 feet long bed. You need to get some plywood from B&Q to form a mattress support.
This is how I created a 7 feet long bed when I was a student. Back then I was on a low income and I moved house each year. For the first years after I graduated I moved frequently too as I changed jobs. The advantage of this setup is it dismantles easily for when moving house.
Its 20+ years since I graduated so I now have a much nicer 7" bed.
Somewhere there will be a very tall young person who has limited resources but wants a 7 foot long bed. I just cannot bring myself to throw the bed rails away. So if you can collect from near Edinburgh they are free. The £30 price is the cost to get them shipped by parcel force. If you want more details please email me, I have more photos and have written a word document which explains it in more detail.