"Salary" for the most part . . . and as far as I am concerned is an incorrect term for this market. Assisting is generally a freelance position. When you get on under a photographer full time . . . I suppose you could be a full timer . . . but generally your title is "Studio Manager."
Photography and the production business . . . in most instances . . . and often unfortunately is a heavy barter and negotiation market. There is no end to it. You negotiate a day rate almost every job unless you are with a regular client. And how well you negotiate and know your market is basically what you will take home.
Some people see dollar figures and think . . . Wow . . . ! Because there are assistants that make $6-800 a day. But . . . they have a decade of experience at least and a rolodex of the top shooters in the world. You may get an asking day rate of that much if you decide to make it your career . . . but take into consideration that a photographers day rate for a decent shooter is anywhere from $2-25,000 . . . the assistant is peanuts in comparison to the production.
If you can carry sandbags . . . you have a good working knowledge of photography. You have a good attitude and work ethic. I would say start your day rate no lower than $150 in a small market such as Dallas. And no lower than $250 in a larger market such as LA, NY and Miami. And up it fifty bucks after about 2 months of steady experience.
If you really need work and are starting out . . . working cheap can get your feet wet. But you may have to cut those clients loose if they are unwilling to negotiate.
Know what your worth and ask people what is reasonable. Most are tired of being undercut and having the market price being driven down by yahoos who think they are doing themselves a service for working for nothing . . . you cannot build a portfolio working for free. Do it for people who you can get something from in return . . . equipment or contacts. Otherwise don't.