Em.. Slant shank presser feet are easy to come by, you can buy all the basic ones at any Jo-Ann's or Hancock or order them all over the internet, so I don't get the argument.
95% of all the quilts I've made have been sewn on Singer 301As, or a 500A. For the money, you simply can't beat the 401A and 500A, they do everything, and they're nearly indestructible. Almost anything can be serviced by technically oriented operator.
For my money, you couldn't pick a superior "heavy duty" home machine. By Singer's account, the 500A is the best machine they've ever made.
edit: Just wanted to mention that I bought my 500A on ebay, and it's still going very strong, even though I abuse the hell out of it daily. I've found 3 301A's at thrift stores so far, ranging from $15 to $55, depending on whether or not they were in cabinets. However, where I used to live in GA, they prices were much higher, so it just depends.