While DS’s and your views and wishes should be considered, you will need to show the LA’s proposed school cannot meet needs &/or it isn’t unreasonable public expenditure.
Costs will only be considered if both placements can meet needs. Although you say they look similar on paper, you should dig deep. It is highly, highly likely there will be differences. Differences in academics can be relevant - this may well run deeper than just exams available. Although that alone can be a strong argument depending on the evidence. Look at your evidence. See what you have and what you need.
Moving on to costs, £55k plus higher transport costs is very likely to be seen as a significant difference. However, you should also look carefully at costs. Make sure all costs are accounted for. What exactly is included in the £25k and £80k? Does the £25k cover all costs? For example, it isn’t unreasonable for LA SS fees not to include e.g. the weekly 1:1 SALT and it need to be funded on top. Does it include the professional time for the AR?
Do you mean DS is due to start Y7 in a matter of days? I hope not! Or do you mean DS is about to start Y6?
More placement appeals are successful than not. However, the success rate isn’t as high as for refusal to assess and refusal to issue appeals.
If you need to appeal, you should also look at appealing B&F as well as I. That is because the placement named in section I is the logical conclusion of B&F. B+F=I. The LA shouldn’t, but it is also likely, to one extent or another, that the LA will write B&F to fit the placement they want to name.