Don't let cruising alone keep you home -I've done a cruise alone - next one coming up in June to Alaska. However, this time I am doing it through singlescruises.com. You pay one port charge and tip charge. I always ask when putting the down payment down that if closer to the cruise I do get a cabinmate can they be added on and always am told that they can - they just need to add the port charges and tipping. I actually did this one time as my daughter decided to go a month before the cruise - no problem.
So - venture out and go cruising.