Once you correctly and positively identify the 'early' MacBook Pro, locating a
replacement PCI solid state storage unit may be the matter of willingness to
pay a price of admission. OWC macsales [ MY UPGRADES ] site has some
fairly good examples that work in more than one portable MacBook/Pro; to
check the exact build model MB/Pro is advised. ~ Note there are some PCI
kits that include an external enclosure you'd not need; that would be helpful
for those upgrading from original to larger, to re-purpose the working spare.
The price varies; you could contact this mac-centric vendor for information
even if you don't purchase. They also have DIY install video links on site.
Note they do have warranty or guarantee, and knowledgeable staff.
Also expect to replace the battery, as it may or may not be viable. If
no other issues develop, the unit may serve you well for a few years.
In any event...
Good luck & happy trails! 🙂