My D'C' are now 18 and 20. I HEed all the way through. I worked (and was the main breadwinner as XP did not work and then became X) throughout our time HEing. I'm going to give you a potted bio so you can get an idea of how it worked for us - your situation won't be the same but I hope you'll get a better idea of how it works and the additional choices that HEing afforded us. It's long but it might be helpful.
When they were very small (until DD was 7 and DS 5), I childminded 2 days per week and also worked PT (but from home, 2.5 days per week, in an IT job). The IT job I did when they were asleep (very late and very early in the day!). I helped run a toddler group one morning a week and DD was very proud (at 6 or 7) to be a childminder and a helper at the toddler group, LOL. We also attended a general, 'social' HE group that cost about £3 per family (per fortnight, possibly).
At that time, we were in SW London. DD attended Girls' Brigade and a dance class weekly - we'd have paid for those even if she'd been at school. They both went to LA sports classes (e.g. swimming lessons) which we'd have paid for even if they'd been in school. We also went to monthly Saturday morning kids' music concerts at the Festival Hall and various other stuff which we'd probably not have done if she'd been in school, because we wouldn't have had the time or energy. IME, in the summer, many HE groups move to free venues - such as parks - which cuts the cost.
When we moved to Wiltshire (when DD was 7 and DS 5), I worked in the PT IT job, was self-employed as a copyeditor and also started to work a few hours a week for the OU.
We got involved in the local HE scene: pottery in someone's house (about £3 per family per session for materials and firing), social meetings in church halls (about £3 per family per session) to cover the hire cost, swimming and ice-skating (cost of the activity to the LA). None of that was as expensive as school (uniform, lunches, trips etc.). It was also far less wear and tear on the nerves - no shouting to get a child on the spectrum out every morning!
We also did summer sports schools, weekly gymnastics and other clubs that we'd have paid on top of school anyway (if we'd had the energy).
When DD was 11, she wanted to learn an instrument and we went to the local Saturday morning music centre (which was very good value for money) plus paid for individual instrument lessons for both DC. Music-related activities was probably our main ongoing cost. I'm not sure we'd have done it if they were in school (because of other calls on our time and money).
DD spent two years at 12-13 doing 6-month exchanges with German-speaking girls. That had associated expenses but it got her a place at university on a Law with German Law course.
I also started an HE competitive LEGO robotics team, which is now in its 8th year (now without me!). The ongoing cost to the parents was minimal - we met weekly in my house at no charge and two families donated the equipment so it cost about £150 pa divided between the team (variable numbers up to 10) plus about £12 per child for team shirts. We had 25-30 young people through that team over the seven years I was coach and we had trips to international competitions in NL and Tokyo (which cost, but we treated it as family holidays).
I wouldn't expect anyone else's HE to look like that (!) but it was not pressured - we had plenty of time to simply chill and the DC learned things that they have kept up to a good standard (such as the music). All the other activities became an integral part of the DC's education and sparked off other learning. For example, we learnt a bit of Japanese before going to Tokyo. We did not follow the school exams model, so we had no need to drop all the life-enhancing activities to make sure we had revision time. For me, the best bit about HE is that the DC have learned that they can do anything they put their minds to and they are not afraid to join in with things. I'm unconvinced that they would have the quiet maturity they now have if they had been through the system - other adults who see my DS in the college where he started A-levels in September say he seems very mature in comparison with his classmates.