The most quiet delightful machine I have ever sewn on is a Featherweight. They can do the zig zags if you have the attachment but are set up as a straight stitch machine. I even have a 1/4" foot. The cost can be low (usually under $300 and sometimes only $100 or less) if you are willing to clean your own machine.
After my second back surgery I have a weight limit of 25# for the rest of my life--which I plan to be another 20-25 years! So I could take my own machine to classes I purchased a Singer Featherweight. Actually I bought three (a 1950 and two 1948's). I love them all. Since they are mechanical I can do all the maintenance on my own.
Just the other day I was piecing on my Viking Diamond and with every single patch I would think, "I wish I were sewing on my Featherweight". After about 6 pieces I realized all I had to do was set this little 11 pound beauty on the table and sew. They are simply a Joy! It is much quieter and smoother than the expensive machines by far.
Grammahunt