Freecycle! Google for your local branch.
You can't do 'loans' but you can place 'wanted' ads. Although I think you have to do an 'offer' first, so it might not be in time.
We get rid of all our unwanted, non-ebayable stuff on it - including a spare travel cot only last month...sorry!
Failing that Lidl & Asda were both doing them for £25 or so last summer.
Alternatively, if the baby is young enough - when ds was 4 months dh took him to visit MIL overnight. She'd ordered a travel cot & it didn't arrive - so ds slept cosily in an opened out family size suitcase, base padded with blankets.