Asda have a reasonably decent quality waterproof mattress for £99 in single bed size and £79 in toddler bed size. These are much more hghly priced on the special needs suppliers sites but so useful!
Sainsburys have a pine single bed with pull out guest bed frame for £99. It looks study enough to fit a bed rail to if needed. Handy if your child is too upset to let you leave the room on a regular basis but you are desperate to catch 40 winks. Study enough for a teen too.
Argos has a nice low level cabin bed with storage for £99 so half price. The bed has highish sides for those who regularly roll out of bed if you use a shallow mattress. It's called the "haven" methinks, but the delivery time is over a month. It looks perfect for storing some of those AS "collections" close to hand if you have limited space. www.argos.co.uk/static/Product/partNumber/7380606/Trail/searchtext%3ECABIN+BED.htm
None of these are "specialist beds" but I thought the info might be handy for others who like mine have no major physical disabilities but are restless sleepers/bedwetters etc. Getting the equipment you need on a limited budget is tough sometimes.
Asda also has a baby care sale on for anyone looking to get some stair gates or saftey stuff like socket guards etc.