We're done with our cot. It's Mamas and Papas, about six years old, VGC save for a tiny scratch or two at the feet. It's white. Entry level new mattresses from M&P start at around £40.
Not sure how much to ask for it. Maybe £20 towards new bedding for the replacement?
Whisper me if you're interested, can send you a picture or happy for you to drop in and see it.