There are a couple of examples online on how to adapt a desk for cutout for a sewing machine. Also check your local Craigslist for people selling old sewing cabinets and sewing tables. I know on my CL they have been selling for $10-$50. There was even someone selling a Koala for around $250.00 on my local CL.
It is amazing what bargains you can pick up on CL.