Charger replacement £229 (typical price, but I actually bought 3 expensive chargers for different situations - not included here - after the original failed)

Upholstery, Arms, various worn / damaged parts £700 (I actually spend £1700 every year completely rebuilding one of my 3 powerchairs but this 700 is a typical figure for an average users bill.
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Motors 1 set £600 Again, this is a typical; figure. Some users will never wear out a motor. I wore out 11 sets in 13 years... In 4 different chairs and three different brands. If you are very active you will wear them out! If you sit at home all day they will outlive you.

Batteries £400 per year. or £1200 over 3 years  Scary eh? Well its true. As a busty ACTIVE user I need new batteries every 10 to 12 months. The very best batteries at £400 a set can give 500 x 80% deep cycles. In a lab with smooth constant currents and optimised charging and temperatures. In real world use you get 300 to 350 cycles or days use and recharge. If you use the chair like my grandma, and sit at home and don't really use its range you may get 5 years! Or if you are worse than I am and flatten the batteries pretty much daily then you will not get 6 months.  

Charging costs every night:
70Ah @ 24V (your batteries usable electrical store) is electrically the same as 7 Amps at 240v for 1 hour. Its the same amount of power/energy. But charger and battery are not 100 percent efficient so 10 amps for 1 hour is approx equivalent at 240v mains power when recharging. That is 2400 watt hours. at a typical UK price of 9p per kW/hour. so just £0.21 daily. or £6.48 Per month. That was cheaper than you expected wasn't it? Well it surprised me!