Experienced Ren Fester here! A good corset is going to be expensive because the materials used shouldn't be cheap, and they are time consuming to make. If money was no object I'd be buying from: Tea length wedding & retro & prom dresses | Corsets | FairyGothMother but those are way out of any reasonable price (factor in the exchange rate). This top one would be very supportive, but again, price: Long Bodices - The Bodicery. I don't know when your surgery is, but if your local ren fest is before then head there and there will be multiple vendors selling corsets, and for more reasonable prices. In WI I've seen them go for as low as $75. In MI they start more around $125.

In a pinch, and if you have very basic sewing skills, you can do this: order one of the "cheap" ($40) plastic boned lingerie ones from fredricks of hollywood. I recommend the dream. Carefully rip open every boning casing and take out the plastic bones. Measure them, then go online and order metal bones in the same lengths. Spiral bones will have more give to them, they're coiled up metal, sprung bones are just a plain old metal stick and more supportive but you will not be able to bend in them. I put sprung next to the laces and spiral everywhere else for maximum comfort and support. Slide those back in the casings, stitch them back shut, and voila, a "real" corset for around $50.