Beth,
I think you raise some very valid points and have said honestly what some moms are afraid to. big {hugs} to you hon as you try to figure out what works best for your family.
For me, it was #1 that I loved breastfeeding. #2 the cost of potential formula feeding. We were on WIC for part of ds' early months, dh was in grad school. I asked about options for formula, and they provided no milk/soy-free formulas. I was lucky to have a super supportive dh and family members, who endured the milk-free thing with me. I knew if I could make it to 11-12 months, that I could supplement with enriched rice milk instead of formula. Ds to my surprise, outgrew his milk intolerance at 12 months old anyway. Dd outgrew hers at about 17-18 months old. I celebrated with pizza, and then fell sick on the toilet because my body wasn't used to it!

With as sensitive as your son is, there is probably no way he would ever tolerate Alimentum or Nutramigen. (If you could even get him to take them at this point) I would guess that either of those (they are NOT milk/soy-free, just "pre-digested" ummm pre-digested by whom?) would actually make him worse. If you do end up going to formula, your ped will need to prescribe something like Neocate, which is corn-based, I believe, and quite expensive. (corn is another huge allergy)
I am going to strongly suggest that you keep your 6 month goal, and really strive for 12 months. The longer you go, the better off he will be, and the less likely his allergy/intolerance will continue through childhood and perhaps adulthood. Is 6 more months worth that? To see him sit at his 2nd birthday and be able to have a spoon of ice cream with his birthday cake? Your odds are better with that if you can keep nursing milk-free than if you switch to formula.
Right now, LLL and WHO are both suggesting that babies be nursed up to at least 12 months. Any pediatrician that is not supportive of that, well, I'd probably switch to a new doctor. Where are you located? Can I find you a local support nursing support group? I know my old support group has a MSPI email list that we can get you subscribed to if you'd like. Or can we help you find out-to-eat choices that make this easier for you? Or day-to-day choices (maybe some new recipes?) that will help? I am happy to help in any way I can.
I always tell moms that breastfeeding gets a ton easier between 8-10 months, usually around 9 months old. They start eating 3 meals per day, only nursing 3-4 times (one being first morning and one being before bed, so it's quite infrequent)
-----------------------------------------------------------------------------------------------------------------------------------
That said.
I was a moderator on the breastfeeding board for a long time. I knew by your first post that you're having a tough time at this. Breastfeeding is a commitment. And having an MSPI baby wasn't something we signed up for. It changes everything from how we cook to how we socialize, to how we feel about food. It is emotional! Completely weaning to formula won't make things that much easier, it will be a different kind of challenge. And weaning is HARD, very hard for some babies and moms, so I know you know it's not the easy road. Dreaming about a new diet is tempting. Being a mom is self-giving, and on top of it you've had to give up chocolate too.
So if you decide to try weaning to formula, know that I will support you through that and help you with that too. Sit down, take a few weeks to think about it, and know that you have time to make a decision. Live with it for a week or so. {hugs}