Linear Tracker ...I was wondering


Is there a not too expensive (less than $¹⁰⁰⁰) and good linear tracking tonearm that I could mount on my SL1200MK5? 


128x128jagjag
Look into the Trans Fi Terminator. Not sure if you'll gain the benefit you seek on that turntable.
Be hard to find anything new for less than $1000. Unless you wish to take a chance on some designs from the UK?
Like this......
https://www.airprodigy.co.uk/

You may find a used ET arm for that price though.