Covers are relative to how you use them and how good a coverage you want.
True custom covers will give you the best coverage but cost the most however if treated right will last a long time. My cover is 13 years old and still looks almost new. Now, i do not use it for outdoor winter storage, however it has sat outside a few winters and has been in all sorts of weather both trailering and parked. Not one scratch to the boat ever and it covers it completely.
That said, if you are looking for a winter outdoor cover, I would go cheaper and just plan to replace it every few years.
My cover cost $6k to make but I got lucky and got it for 1/2 price less than a year old. It was custom made for another Comp just like mine.
The other factor is how long do you plan to own the boat. If you plan on keeping the boat for a long time, maybe a custom cover makes sense.