Sculling would be a good temporary measure. You'll learn a new (simple) skill, and it'll cost you probably $100, instead of $1000. I'm sure you can temporarily attach a lock of some sort to your stern rail. I'm blanking on the name of the couple who have used this technique to cruise their heavy 30-something-footers all around the world for decades, with no engine aboard Taliesin.
Lin and Larry Pardy.