A better way is:
#!/bin/bash -xv REM_DIR="/home/jan/rem-dir" SSHOPTS=(-C -c arcfour256 -o "ServerAliveInterval 15") SSHUSER="jan@example.com" REM_FILES=`ssh "$" "$SSHUSER" "find \"$REM_DIR/\" -path \"*lost+found\" -prune -o -type f -printf \"%P\\n\""`
The main problem was with $SSHOPTS, the trick is to put each argument in a separate element of an array.
@Dennis thanks for the useful link.