DIY installed and self certified a MVHR for less than £1500 four years ago, so more like £2k now. No need to spend £10k on a simple system, like everything we get carried away with specifying equipment. The only thing I would do differently is fit noise attenuation, there is some ‘cross talk’ between rooms although only noticeable when it is dead quiet in the middle of the night. Rather than looking at the most sophisticated system, start from trickle vents and think what would be better than that? DM me if you want details of equipment.