I used clear packaging tape to tape a small crack/split in my Boxster's rear window. It kept water out when it rained or I washed the car. I never put the top down with the tape or it would not have lasted very long at all. (The window cracked when in cold weather I tried to put the top in its service position and didn't do the "chop" quick enough.)
Finally had the rear window replaced at a highly recommended auto upholstery shop in the next town over from where I lived. The cost was IIRC $600. The new window was the same heavy plastic as the factory window.
Can't recall now when I had this done but it lasted years and years. Finally the top started leaking. Priced a factory top and with a discount it was around $2500 (list was over $3K) and labor would have brought the total cost up to near $3K. Too much to spend on an approx. 12 year 250K+ mile Boxster.
Elected to have a GAHH top installed. I stayed with the plastic window and the cost including labor was IIRC around $1400. The top was high quality and was fine when I sold the car in Dec. 2017.