I'm West Sussex/Surrey boarders
DIY Livery: £180 pcm at a non-fancy yard but has good winter turn out and really good hacking.
Assistance: £25-100 a month. Closer to the top end at this time of year, at the lower end in the Summer.
Feed: £85 for 4-5 months
Supplements: £33 a month.
Hay: £40 a bale which lasts a month in winter
Bedding: £25 a month
Insurance: £38 a month
Barefoot Trimmer: £120 every 8-12 weeks
Lessons: £45-90 depending
Competitions/clinics: £10-45
Mines a little harder to quantify monthly, as I don't pay for feed, bedding, hay or my barefoot trimmer monthly. Some months I might do two clinics and two lessons, other months I don't do any. Some months I might need to buy or replace equipment, other months I don't.
I would say on average, he's about £350- 500 a month but that doesn't include the cost of quarterly physiotherapy sessions, equine dentist, vets or my off road riding permit.
I do keep a spreadsheet, so know what is spent on him. My OH also knows ...
I know Pete is worth every penny, I'm unsure if he thinks the same