Shoulder entry suits are almost always less expensive than an identical suit with a self donning type zipper. The zipper is longer with a self donning design and I suppose they are perhaps a bit more expensive to manufacture.
The obvious advantage of a self donning suit is that you can put it on by yourself. But it does require a bit more shoulder motion and a diver with a shoulder injury or restricted range of motion may have some trouble getting into one. Also, in many self donning designs, the zipper extends below the waist and the zipper is subject to wear from the weightbelt and waist strap. This is reduced but not entirely eliminated with a flap protecting the zipper.
The biggest disadvantage of a self donning suit in my opinion is that the torso needs to be cut a bit longer than in a shoulder entry suit and fit is often not quite as good in the self entry suit.
Some models are just a bit too long and require you to bend your neck quite far forward and down to get into the suit. (if you have a neck injury, this design is not for you) Getting in the suit is usually worse than getting out as the underwear compresses a bit during the dive and you get a little more head room to get out. They tend to get more restrictive as the underwear gets thicker and a good fitting suit of this design will not be very tolerant of weight gain in the mid section.
Other self donning suits use a telescoping torso with the extra lenght folded over and secured with a crotch strap during the dive. They are easier on the neck to get into as you can lift the neck seal well clear of your head. But they have the extra lenght to deal with in the middle and may be a bit draggier in the water.
With a shoulder entry suit, you virtually always need assitance to zip it up (although a solo exit is possible) so it is a non starter if you are a solo diver. Also, the zipper across the shoulder can sometimes make the suit feel a bit more restrictive when moving your arms forward in front of you although this is normally less apparent in the water than on the boat.
There have been a few drysuits made with the zipper placed horizontally across the upper chest. This potentially offers a self donning suit with the shorter torso and better fit of a shoulder entry suit. In practice, it is possible to get into one by yourself, but it is difficult. And unfortuntely, the placement of the zipper causes more resistance wehn moving your arms forward than any other design as the zipper does not fold on itself and is essentially in the way when you move. I don't see this as ever really catching on.
It used to be that the longer self donning zipper cost more to replace than a shoulder entry zipper but last time I checked the cost was the same ($235) regardless of the zipper.
So my thoughts are that if you dive solo and really need a self entry suit, it's worth the money. Otherwise, save some bucks, and get a potentially better and more streamlined fit by staying with a shoulder entry suit.