I totally agree with you about the cost of Steiner. I've got a friend who home schools, and she'd love to send her kids to Steiner, but said 'only the rich can afford to be peasants.' I happen to agree with her.. though there is now Govt funding for more free schools to open, so things are continually changing here.
I totally understand your reservations. If I were you, I'd work out what all the options are in the area you're going to move to. It can vary hugely in the UK. I personally don't like church schools, for example, but our three nearest primary schools are all church-sponsored.
When you know where you'll be, there'll be people on here from that area who can give you first-hand opinions on the local schools, and what provision they have for E2L (English as a second language, as it used to be called..) It can be very, very good in more diverse communities - usually inner city. In rural communities, a bit patchy. e.g. a little boy from Poland has just started in my daughter's rural school. Much as they try to give him help, I do think it's been a huge culture shock for him, though they phased in his attendance (he did half days for two weeks at first). Nobody working in the school speaks Polish, but despite that he has done extraordinarily well, and seems to thrive most during playtimes and with games generally where there is less formality and more laughter (less pressure to 'get it right'.) (Am ex-primary teacher, so have some working knowledge of the way schools here work. Also moved here from Australia, so understand a tiny bit about the shock/excitement of moving here.)
If you manage to find what you consider to be a good school, so much of what is good about Steiner is applied in mainstream too. Our school uses the outdoor classroom a lot, and does a less formal style of activity in the afternoons. Wish they did more of the arts and PE, though - that's what I think has been squeezed out the most by the National Curriculum pressures.
Come here for a visit, go to see all your options with DS. You'll have an instinctive response about all of it, and so will he!! Whatever you choose (even home schooling for a while?) if he gets to know some of the children who go there before he starts, he may find it far, far easier.