Needs will almost always come before wants. When it comes to Transhumanism, the ability to differentiate the two tends to blur, because a need could also be a want depending on the various methods of achieving a need. There’s the “getting by” need and then there’s the “thriving” need.
For the disabled, this dichotomy determines how well they’ll get by in life. If someone loses a leg, then simply getting by could be achieved with a cane, a walker, or even a low-tech prosthetic. However, if this person wishes to thrive in life, then a high-tech prosthetic would be much more preferable, though could also be considered a want rather than a need.
For Transhumanism to work, however, I’d argue that the ability to thrive should be considered an absolute necessity. Thus when it comes to the disabled, I believe they deserve the ability to reach post-humanity before anyone else. In all actuality, this is already happening.