We had a supervisor and consultant and did all the tutoring ourselves for 6 months, then hired a tutor for 6 hours and continued doing the rest ourselves
We had 2 hours a week supervision (so about £400 a month @ £50 p/hour).
We had to pay upfront for a 3 day workshop and initial testing etc (£1500) and consultation was £150 every quarter. So about £7500 for the year. We also paid for a private EP and some legal advocacy fees for Tribunal (added to mortgage).
DS was 3 when he started and DH and I managed 15-20 hours between us a week. We were able to achieve enough progress to win at tribunal. DS continued to go to mainstream nursery 3 half days and get LA provision there and we compared the two and proved much more progress.
Our programme was def not as good as a professional one would have been and we seriously flagged in the second 6 months leading up to tribunal (stress, paperwork and sleep deprivation did not help) and I was more than ready to stop. But even though we were only average therapists we were still much much more effective than the nursery staff. It was enough progress to win at tribunal and we then won a 35 hour per week / 48 week per year programme so worth it.
We used DLA. My mum gave us £200 a month. We eventually got some direct payments and hired a student who wanted to train in ABA for a few hours. Sometimes people can get students at low cost or free (eg psych students from a local uni) or ask family members to do some (not an option for us). Eventually we got the supervisor to do some training in nursery (once we had enough evidence that they were not doing a good job without ABA) and that improved what happened in nursery sessions too.
I think its hard for a parent to do it long term, but for us it was worth doing it for a year to get through appeal / tribunal. It was easy at the start as we just had about 6 programmes - now DS has about 20.
If you have a limited amount of money it can be worth starting off yourself and then hiring tutors once you start to flag. The supervisor was crucial for us and worth every penny.