I’m not sure about cost, but I know that when my parent’s hosted an event, they found that it was only very slightly more expensive to buy everything at IKEA than it would have been to rent it. This was an appropriate choice for them because they have storage space for the stuff, and host events frequently enough that buying everything actually saved them money in the long run. However, if you rent, the rental company brings clean dishes and takes away dirty ones. If you buy, you have to wash them yourselves.
Long story short: If you do this kind of thing frequently enough, look into buying dinnerware from ikea. If it’s only a one-time deal, go ahead and rent.