Multimac will set you back just under £1500 for the 3 seat version with 2 minimac seats (appropriate for 19 month old and newborn) and headrest for 3.6 year old. I haven't got one but we are contemplating one for our four children. I think what is attracting me is the safety. The older children will be in 5 point harness', the younger two in rear facing seats for much longer and the whole thing is fixed in the car much more safely like with isofix seats. I have to say I am tempted and am selling my wedding dress to attempt to pay for some of it! We have a four year old and 3 year old and 3 month old twins and drive a Multipla. I dislike having two children in the front and would prefer to have them all in the back.
Ive just been looking at these as i didn't even know what they were! They look great! We currently have a vauxhall zafira but have been looking at bigger cars, Mercedes Viana and Hyundia i800's but this may be the answer to our prayers! I wouldnt like to install it though, it looks complex, have emailed them to see if they install anywhere in the UK