Let us know how you get on, OP - and maybe contact the poster of the thread you linked and ask where she's up to and how much it's cost so far, to give you more of an idea? Hers is totally different to yours, and she seems to have had some evidence as well, but you might get a ballpark figure to work from, as long as you double it to include your brother's likely costs.
As you said above, none of us have seen your evidence, or even know what that evidence is. Bear in mind, if the judge gets as frustrated with you - your brother won't necessarily be cross-examined, even though you want him to be, and a stutter is proof of nothing (no matter how much you want it to be) - it really will not go at all well for you.
You have not answered whether your family, who are egging you on in this, are contributing to your costs, despite being asked several times, so clearly they aren't. I don't know whether they are just a bit dim, or whether they are loving the drama by fuelling the rift between you and your brother, but they don't have your best interests at heart bases on what you have written here.
Be very careful OP - none of us know you, but no one with half a brain wants to see "a skint single mother" bankrupt herself and permanently damage her children's future, especially not to fulfil family members' cravings for gossip and drama, fuelled on fantasies and wishful thinking. Your best possible outcome can come from mediation, if your brother agrees.
Your insistence that black is white in the things that you are cutting and pasting is actually quite worrying, even though you don't have legal training - it's really a matter of basic comprehension skills. It would probably be a good idea to take a trusted friend with you to the solicitor, so you don't end up like the person pp mentioned, who ended up years do the line and well out of pocket. That solicitor had put in writing her reservations, but the litigant had wilfully ignored /failed to comprehend, and though the only possible recourse she had would have been to go after the solicitor, even that door was closed.
Be careful, OP - no one here wants you to end up a sad face story/in contempt of court/bankrupt. We don't know you, we pity you being in your situation, and we have literally nothing to gain by warning you to look after your children and yourself above all else. If I thought my mother had placed us in a vulnerable position that we didn't need to be, to satisfy her anger, however justifiable that anger was, in would judge her very harshly for endangering us.