I thought the price was way OTT for what it actually is. Maybe I should make one.

We've got one and have put protectocote (spelling going silly this afternoon) on the plank so that it blends with the boat. Fortunately have not had to use it in real emergency but as we have friends who seem to make a habit of saying hello to the water then it is reassuring. Price wise - seen them from £80 to £100 (ladder i mean not friends)
The plank is detachable from the ladder so whilst rescuing someone using the ladder one's other half could get off the boat to ring the emer services !!!
Ken & Carol of miracle leisure can give you the spiel if you want!

Came across someone else thinking of making aluminum gangplanks.

My requirement would be a aluminum frame with a wooden tread along its length, maybe painted in the same colour as the boats upperworks. Target price £49.99 plus a nominal optional amount for painting ??

I would pay extra for a pin at one end that would anchor the bank end to the towpath and stop it dragging when the boat surges with passing boats !!!

I've just looked at the Miracle Products one which has a chequer plate infill (not my preference) and it is now £98 plus p+p

This looks like a ABRU ladder to me with a piece of Ally grip plate. Search the DIY sites for ABRU products.

You can buy a 2 piece ABRU ladder for about £35 in B & Q or a few quid on eBay. Presumably, you could separate the two bits, buy some sheet aluminium and make two ladder/ganglank combos for, say, £30 each?

That's what I'm going to do.

A man after my own heart