Call BIP or Eurocharged and get good 550cc injectors for a lot less. (E55 forum) Put them in yourself or find a reasonable mechanic. Tow it somewhere else. White smoke is water, either in the gas, intercooler leaking, or head gasket. Head gasket problems are rare. I would start with a bottle of dry gas in the tank. If that didn't help then pinch the hoses to the intercooler. It seems unlikely that injectors will fix your problem. Do to age and mileage you are due for a fuel pump and sending unit. The filter gets clogged and the plastic housing starts to crack and leak. You don't want that price from a Mercedes dealer. If you don't smell gas in the cabin after a fill up it's not cracked yet so put your Techron in to improve the filter after you deal with your current problem.
If your injectors truly are bad, it's no big deal, buy some used ones on Ebay, and get instruction from Youtube. Remember, the E55 is the same engine and running gear, but they are way more popular, so search for e55 parts and info.
Oh, and welcome to the board!