SSD's don't cost a lot and it's pretty easy to upgrade a 2011 MBP. I upgraded my 2011 MBP years ago and it made a lot of difference over the standard HDD, but before you go rushing out to buy one, what part of your system is slow. If it's boot times and time to open apps and files then and SSD will do the job. If you are doing something that requires loads of RAM or maxes out the CPU then you might need to replace the laptop. do your normal stuff and have activity monitor open and see where the performance issues are before buying anything. If you do decide to go for an SSD the Samsung Evo's are pretty good.