A variety of textures are good candidates for sisterlocks (which is a trademarked method and must be done by a certified sisterolocks technician), including relaxed hair!
Sisterlocks are often chosen for their aesthetic. They are very thin, so from a distance they appear almost like brushable straight hair, which matters to some people. This may also be a way for someone to have locs in a workplace that typically wouldn’t accept locked hair. I have heard of some women in the military being able to keep sisterlocks, for example, but that was only what I’ve read online.
Being a trademarked technique, sisterlocks are pretty expensive. However, from my hair cultural background (straight, silky hair texture), spending more than $30 on a haircut and $5-10 for some shampoo and conditioner and other supplies now and then seems outrageous.
For people from the other end of the spectrum- folks who keep natural kinky, coily, tightly curly, or afro textured hair, spending a substantial amount of money on the hair is pretty normal.
What seems expensive is really relative depending on where you’re coming from and what you’re used to.
For a sisterlocks install, the lowest prices I am seeing online are somewhere around $400-500+ and that is on short hair, so starting sisterlocks is a substantial investment. Thereafter, I am seeing monthly maintenance costs of $60-80 or so. This probably varies a bit based on where you live.
Depending on you, what you’re accustomed to spending on your hair, and what you have available to spend, that may seem reasonable or shocking!
However, if you truly are in love with the aesthetic of sisterlocks and feel that that is a hair commitment you want to make, look up a local sisterlocks technician and go in for a consultation. You may find it worth your while, or you may prefer to have more traditional locs in your hair.
I hope this answers your question and I hope I was polite and respectful enough talking about costs and perspectives!
Go with your heart- if you truly truly want sisterlocks, then get them. They may be a substantial monetary investment, but so is a tattoo, a car, an iphone, etc.
If you would like to save money and have thicker locs that look more “traditional,” then I suggest you look into some other methods.
At the end of the day, all locked hair that is well cared for is beautiful.