Monkey3:
If you want to PM me your address I'll send you one of the rs 485 modules if you want to have a look. No pressure but definitely the least I can do. And I very much doubt I'll be using them.
Thanks for the offer, I'm also in the UK and the cost of shipping will be way more than the item is worth.
A quick look at your github write-up and depending on what else your going to hang of the Mega I/O pins you might be okay with a Pro Micro. It is a lot smaller than the Mega and has native USB built in for serial debugging so the hardware UART could be used for the RS485. I use them for various DMX projects as like your project I needed Serial to the PC and hardware serial for RS485 (DMX is 250000 baud)