A few years ago, I went to change my sennheiser headphone cushion at Alexandra and paid SGD55-70 just for the replacement and workmenship. After 1 year plus, it melted again. Perhaps Singapore weather has caused the melting or the original sennheiser ear cushion is built such as not so lasting. After changing the cushions twice, I decided to switch to Beats Studio Headphone since. I am still using it perfectly.
I am not sure if the prices has changed, you can call them to check the price first. My suggestion is I always go for the original replacement as the third party brand may not be well fit.