There are way cheaper tumbers that do a perfectly good job. Its not rocket surgery. With your small volume I would consider a 2-chamber tumber (one actively adding, one breaking down). Should not cost more than $85 US (so maybe around, GBP 60?

https://www.amazon.com/TUFFIOM-Composting-Capacity-Chambers-Rotating/dp/B08J46TTQX/