We've home educated all three of our DC (it's called Home Education in the UK despite what the rule makers in the government would like to call it 🙂).
Eldest two are NT, youngest has SEN. Like a PP said, it can be as expensive as you'd like it. The biggest financial consideration is how it impacts your own/your partner's earnings. We opted for me to not go back to work once eldest was born but I could have continued to do the self employed work I used to do, around HE.
Clubs and activities are only probably as utilised as much as you would for a schooled child. For young children it isn't remotely expensive because the goal is to keep them engaged. It would be daft to fork out for expensive online resources for a 5 year old when 5 years olds are very likely to get bored quickly.
We used Reading Eggs in the early days and various 'fun' and free other resources like BBC bitesize , conquer maths etc but mainly we read to our children and they learnt so much from the world around them. Crucially it was VERY child led. We kept it fun and therefore they enjoyed it and learned from it! Anything boring, they switch off and learning doesn't happen.
Once our DC got closer to GCSE age, there was no burn out and boredom, they were excited to pursue new things and those a GCSE or two to do. This was around the age of 13/14. Gradually and staggered over the next few years, they achieved the necessary GCSEs that enabled them to go to college/sixth form. All self studied.
GCSEs obviously cost money and this varies across the country and is exams centre dependant. How much you spend on prep is also personal and varies. Much of our DCs prep and revision (for subjects like maths, geography) was using past papers which is the cost of printer ink and paper. Also buying text books.
To make an important point, my eldest is using the printer as much now she's at sixth form as she did when she self studying at home for her GCSEs! And needed a textbook recently suggested by one of her teachers which cost nearly £50!!
Uniform costs and the back and forthing costs are less with HE too.
You're a facilitator, you're not and don't need to be a teacher or recreate school. Children have been learning since the beginning of time. School is a relatively recent concept. The key for us was keeping children engaged and learning never becoming a chore. This we believe we achieved without the possible trauma of school.