Hi there,
I was wondering is it possible to set up and run a Discourse community for small scale use completely free of charge or are there neccesary costs at some stages?
Discourse is an open source software and is free to use. In a self installation you will pay only the cost of the server that hosts the site, for example Digital Ocean has plans that start from $5/mo.
Take a look to Recommended Hosting Providers for Self Hosters
Is there any way of fairly simply running a server for free. It’ll be fairly low traffic?
Ultimately no, if you ignore sign-on bonuses.
tbh the higher cost by far is the time you will happily forego proper work and sink into it instead 
If you are successful you might be able to cover costs by member contribution and/or affiliate marketing.
Nothing is free, and software needs to run on something. $5 a month for a small Digital Ocean droplet is a pretty great steal. I run mine on a DO droplet and have zero issues. My monthly cost with image upload space is $15 a month.
…and Digital Ocean isn’t even the lowest-cost VPS out there. I use Contabo (whose lowest-cost tier is about the same as DO, but gives you quite a bit more in terms of CPU/RAM/storage), but these hosts seem to offer a basic VPS for $30/year or less:
https://clients.budgetnode.com/cart.php?a=add&pid=77&billingcycle=annually
https://freerangecloud.com/cart.php?gid=1
I don’t see a way that “free” Discourse is going to happen, but it can be very inexpensive.
Thanks for all the responses. Much appreciated.