How do I convert a sofa table to a kitchen island?

Why bother? Excluding Hardware, the Material Costs $35 extra (usually in hardware) to integrate it into the Design than to exclude it.

To integrate the Excess Materials, rather than the Hardware only, to let that be for something else, like: a Donation to a Dog Pound, is always senseless, really.

It might differ if it was a cast iron tub you don't wanna haul to the curb.

Few however make a Kitchen Isle out of a Cast Iron Tub.

Anyways, when you sum the expense of online designs, and your budget, you likely are better off looking at the

Designs at: Hayneedle.com and either

A. finding one in your budget to purchase it

B. Attempting to reproduce it of something similar by comparing that item to Designs available online.

Do you have a picture?

I turned our old table into an island with stair balusters. So easy!! Here's the DIY if you want to peek. https://www.exquisitelyunremarkable.com/2013/06/decorating-cheats-farmhouse-table.html

Just set it there. You can add a new top and towel hooks, make it suit your needs.

Here is a post http://designingdomesticity.blogspot.com/2012/11/diy-kitchen-island.html