There are formulas that are partly hydrolyzed. Maybe this is what you have now. The ones I mentioned are "fully" hydrolyzed. Allergic and refluxing babies tend to do better on them. These formulas still have traces of intact milk proteins in them though. The MOST hypoallergenic are the formulas made just with amino acids. Many babies finally improve once they get to these. Amino acids are the building blocks of proteins, without ever having lived together in a cow : ) Neocate and Nutrimigen AA are two of these. These are very expensive, but he may be able to depend more highly on low-allergen solid foods in a few more months, so your cost can go down a little each month. Cost-wise, I think I'd try the soy first -- whatever seems right to you. If you have a baby who really "wants" to be allergic, it's possible that he'll tolerate soy for a while (or not) and then develop a sensitivity to it as well. You'll know if/when it happens, and then you can go for an amino acid formula. The doctor offices should have free samples of these various options...
Some babies really don't like the taste of the hypoallergenic formulas. You can add a pinch of sugar to start, or maybe a tad of apple juice. Then you can usually gradually reduce and stop these. I think most are happy with the taste of soy formula.
Unfortunately, they started putting non-hydrolyzed corn products into the hydrolyzed milk and the amino acid formulas several years back. Some babies react to corn as well. I guess it's in all the soy formulas now too. The liquid, Ready-Made Alimentum is (unless they recently ruined it too) the only one without corn, but again, it has traces of milk proteins left, because the hydrolysis is never fully complete. Let's just hope that corn is not a problem.
When you start solid foods, you will want to go very gingerly. You may want to avoid any cereals or grains in the beginning. Yams, sweet potatoes, squash, avocado, bananas, persimmons, pears, carrots, artichoke, spinach, and turkey are some good low-allergen starters to try -- one at a time. Rice is generally the gentlest grain, but some babies react to it as well, and it seems to especially be the ones who start it very young.
You could try giving baby some daily probiotics. These are the beneficial bacteria found in yogurt. There are liquid probiotics sold for children, or you can shake the powder from capsules into baby's formula. Probiotics likely won't give you any immediate improvement, but they can help to heal his little intestines over time. You wouldn't want "real" milk yogurt, but there are soy, coconut, and almond yogurts out there that you could try out some day.
Let me know how it's going.