Inexpensive car cover that almost fits
 

I have a 1.5 car garage and 8.5 cars. I have tried a variety of cheap car covers. The few covers I have purchased for under $50 (made of pressed polyester) have all fallen apart within 6 months. I just got one from Amazon that looks like it will do well. It is actually made of a good quality woven fabric (looks similar to a heavy duty cloth shower curtain). The fit is a bit long in the back, but the length and width are good. The mirror pockets fit with a slight pull. If you keep your car outside and do not want to spend $150+ for a proper cover, I highly recommend this for just under $25.
Covercraft Custom Fit Car Cover for Select Ford C-Max Models - WeatherShield HP (Light Blue)
http://986forum.com/forums/uploads01...1442976045.jpg

http://986forum.com/forums/uploads01...1442976065.jpg
http://986forum.com/forums/uploads01...1442976080.jpg

If you are going to use a cover that doesn't fit properly I would suggest putting some bungee cords on it to hold the cover tight. A cover that moves too much in the wind will destroy your paint over time.

Fit looks terrible! If you can afford 8 1/2 (?) cars, you can afford a good quality cover. Where I live, the wind would ruin the paint job in short order if the cover didn't fit well. I'm going on 3 years on one of these and I'm very happy!

California Car Cover Company - Car Cover Materials

Yes, the fit in the back is bad. That is what I was trying to show in the picture. For me, it is not hard to adapt the rear to make it snug. The front fits pretty well.
This is a WeatherShield HP material cover for $25. The cost for one custom fit for a Boxster is over $300 more than this costs.

http://986forum.com/forums/uploads01...1443030803.jpg

I'm getting one for my 996 and will see how it fits. Since a 996 is a little bigger in the back, it may be a good fit. Worst case, I send it back

I picked up a slightly used OEM Porsche cover of of ebay for 125.00 Fits both my Boxster and Cayman depending on what one I am driving. Its not as cheap as the one you pictured but it fits like a glove and is easy to put on. After having the cheaper covers this one was well worth the money paid.

I've used Covercraft for many years; well made, long lasting, stores well...