I have had no real big problems with my 280C and found it reasonably inexpensive to operate.
There are a few 280 models for sale at reasonable prices 50 - 80K Sterling and I would think about going for one of these if you can, it has the turbo which helps in hot and high (although even that struggled to get my fat ar$e off in the middle of summer
) and has a lot more power. The early 28a can be a bit short of power in the summer or 2 up and probably never goes 3 up.
The only other downside is the increase in fuel consumtion over the R22 but you can get better than 1 litre/min by leaning it.