Advice needed: want to buy 50mm 1.8D for d3100

I want to buy nikon af 50mm f1.8D for my D3100 body and i know it wont auto focus on my body .....

I have tried manual focusing through my 18-55 kit lens whoose focus ring is not very good and it was a hit a miss type of experience ...

I want to ask how much is the difference between manual focusing through the 18-55 and 50 mm lens
and given my previous should i go for it?
i cant afford the AF-s version
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Adnan