Cake... you didn't see me on my borrowed bike in Market Drayton in the late eighties?
A borrowed bike... and found out on the day that helmets were compulsory... and had to borrow a climbing helmet. I looked absolutely ridiculous 
But you raise a good point... you can use equipment that, if you're not bothered about it costing you a little bit of time, can be very cheap.
There are some ridiculously cheap wetsuits on ebay 18 quid for a new 2.8mm neoprene wetsuit... including delivery. I've never tried one - it might slow you down a bit compared to one costing several hundred pounds... but you can have a go. And if you're in a pool, even that isn't needed.
Running shoes.. 50 quid will get some half decent ones. Bike - well you can buy second hand... and again, you can get an aluminium framed one for 200 quid that won't be as ridiculous as a butcher's bike!
I guess the ongoing costs include your swimming pool entry.
Hope you can do it.