The thing about young children with ASD is they typically cannot concentrate without support - which is why they need a high level / fulltime 1:1 to keep them engaged. That said DS had fulltime untrained 1:1 for a year and learnt nothing, so its also about having the right strategies and programmes in place (ours was left adrift by SALT and outreach).
All mainstream nurseries can get funding for 1:1 without needing a statement. The nursery should contact the area SENCO and ask what is available. My LA puts in 75% 1:1 as a maximum without a statement so DS got 10 out or 12.5 hours funded. If its a school they get the money delegated usually. If its a private or voluntary nursery they usually have to apply.
The most useful thing to get across is that he is not learning. He will not learn much from the environment/other children. There is this idea being in the room with mainstream peers will rub off. It rarely does. Your child might need skills other children just absorb to be directly taught. That takes time. And he is delayed so he needs more learning time than the others, not less.
The way I look at it is other children learn from the minute they get up in the morning until the minute they go to sleep. They learn by watching others and asking questions and demanding your attention constantly. Children with ASD often only learn when someone has got their attention and is directly teaching them. So the gap between the 12 hours the other kids are learning and the few minutes the nursery will give your child is already massive and the gap is widening every day.
So the best advice I can given you is to refuse to accept the notion they cannot fund 1:1. If they can't tell them to ask the LA who can. The other suggestion would be to get them to read a book eg Hanen "More than words" or one specifically geared at nursery children with ASD (there are loads of books written for nurseries). The SALT and outreach may be great, or they may be rubbish - the nursery cannot sit there and expect others to come along and tell them what to do they have to educate themselves what to do.
Your child is entitled to an appropriate education and the Local Authority / nursery have a duty to provide it.
You can also ask them to get an specialist early years / autism outreach teacher in to give advice.
You might also be able to get portage at home (specialist play worker).
You also want to set clear measureable targets eg if there is a language targets make it say within 3 months DS will be able to ...... Rather than something woolly.
And tell them to tempt him to use his words eg withholding his favourite toys on top shelves etc. www.teachmetotalk.com has ideas about helping with language.
And advise them if he is doing the same thing again and again or sat with the same toy - thats repetitive behaviours (stimming) and he needs to be interrupted and redirected or he will be even harder to engage
Good luck.