What you are offered as a place by the LA depends entirely on what area you live in, as not every area has the same provision.
I can only say what we did for my dd - it may not be appropriate for your dd.
We did not want mainstream at all. We did consider an ASD unit based at a mainstream school, but only if dd was allowed to stay at the base for as long as necessary, rather than a drive towards inclusion from day one.
dd has ended up at an independent, highly specialised SN school. it is right for her. she would never have coped in mainstream (may have done in a unit if the place was right for her - I am not sorry we did not push for the unit we looked around, though, as it would not have worked for her)
Some thigns we considered during our school choice period:
we did not want dd to ever feel as though she was failing. she finds life difficult enough as it is, and does not need it highlighting that she struggles more than the majority of her peers.
we wanted a highly individualised curriculum for dd. oen where she can still be working on P scales for writing, for eg, yet NC level 3 for maths. this is achieved at her current school via a mixture of methods - partly 1:1 tuition, partly being able to mix up the groups easily (so she is in one class, but then a separate group for maths, another separate group for handwriting, another separate one for literacy - all based on ability rather than age)
we didn't want dd to have to 'fit in'. we wanted her school to be a place where she felt happy, secure, and enjoyed being. not where she was stressed, having to cope, and 'get through' the day.
take some time to look around all the different options you have in your area. make a list of questions before you go to look around. try to 'see' your dd in those different placements - think through how she would feel and react in the settings you see.
I understand your worries about transport. I had the same, but luckily I am able to take dd to/from school myself, as her school hours fit in with my other children's timings. Others on this board have successfully used transport from the beginning. Again, what works for one may not work for another due to differing needs, so this is another one to think through carefully.