Originally posted by excanonfd I think you would be hard pressed to generate $400.00 even if you sold all of your lenses, especially if your 55~300 is a DAL kit lens and I have yet to see an A*300/4.0 for $400.00. If you are satisfied with the focal lengths of your M primes, start replacing them with A equivalents one at a time. This way you are still able to shoot as normally as possible. Having only 18~55 zoom and a 300mm prime leaves gaping chasm between focal lengths that will leave you frustrated. You may have to dip deeper into your your wallet if you decide to pursue A*300/4.0 later on, but being able to shoot as you've been accustomed to and to continue doing so, is more important than saving for one long lens.
A*300/4 for 400$ is a bargain...here in EU it costs 400 EUR. It's quite steep price for MF lens....so I went for bit cheaper and optically identical M*300/4. This lenses are great, I'm often amazed by the pictures I make with M*.