Dont want to get into a best engine bang here but here are some thoughts
Ralph at
www.rcignition sells a 46cc engine complete with electronic ignition, muffler and engine mount shipped for about $400.00
www.RCshowcase sells a ZDZ 60 for I think $459.00 pluss shipping, You have to get a muffler for it and with a little work a $30.00 muffler from B&B will work.
I have found that if you can get a engine with electronic ignition for around the same range as a magnito engine go for the elctronic.
Just my thoughts
Thanks
Milton