the costs issue is a tricky one - it obviously all depends on:
how complex the case
whether the LA are going to listen to the (legal) voice of reason, or push it all the way through to tribunal, and then beyond
who you take on to represent you.
and advocate is vastly cheaper than a solicitor. FS has been mentioned here, and I have heard good things about her. I know of another one too - can't recall the name now but could look it up - who managed a friend's case incredibly well, and comes highly recommended.
We used Ormerods initially, and I was not massively impressed, tbh. Levenes (Chris Barnett, as mentioned upthread) were recommended to us by: the school we wanted dd1 to go to, our ABA consultant, and our indepedent Ed Psych - we went with them as wanted a 'team' who had worked together before on a simialr case to ours.
Levenes charged £220 +VAT per hour of work on the case. Our LA settled before Tribunal, and so we were spared the couple of full days work and attendance that woudl entail, and costs were:
time sepnt ont he phone chasing case officers
time spent sending (mostly routine, once our case had been discussed and agreed upon) letters
etc.
it cost us a few thousand (sorry not to be more precise, it was a couple of years ago and I try not to remember in too much detail as it was obviously a very stressful time) but not as much as we had anticiapted, thanks to early settlement, which in turn I firmly believe was down to how our case was presented (and by this I mena the whole line up of witnesses, so consultant, Ed Psych, independent OT and SALT, etc - all of which added a few more thousand onto the total. not to mention the fact we were self funding at the school we wanted, so as to prove suitability)
it is not a cheap exercise, and we were lucky to have the savings to liquidate. we have already reaped several times what it cost us, though, as we won the provision we needed for dd1 (and I do not mean reaped in purely monetary terms - the right provision has meant so many gains in development for dd1 - priceless)