Great question and I wish general surgeons talked more about this. I am an attending now and doing per diem locums full time for 1-2 years. The pay is highly variable but the market rate is around $1200 a day to include 4 "gratis" hours and then $150 per hour after that. This is the number that companies like Weatherby will give you. Assumption here is home call, no clinic. You can be presented however at any number that you want. I asked a recruiter last week and she said $1200-1500 was the average, but now $1500 is more commonly a start and $1800 on the high end.
You can ask for anything though, including less hours. Personally I think that paying a surgeon $50/hour to provide 24/7 gen surg coverage is a steal for hospitals and is a reality largely because general surgeons have undersold their skills more than any other specialty period. We 100% should be demanding more as a specialty. Nearly all the subspecialties demand higher pays. It is sad that we compete against other so much.
The highest rate I negotiated was accomplished not through a company, but directly with a hospital and that was for $3600/day flat rate, home call. I did not get extra to come in but still this was excellent as I would often work <6-8 hours per day, and often less on the weekends. That's $25,200 per 7 days/ week. Full disclosure this did not last long as the hospital quickly got someone else cheaper. Urologist regularly make this much doing locums.
I think north of $3K/day is what we should be requesting as a specialty. Those making less than $1500 a day are in fact earning less than mid MGMA full time surgeons. And that is with way more call + all the inconveniences of traveling/being away from family, etc.
The highest I've seen an agency promise as a flat fee is $2K with no extra for callbacks.
One of the frustrations is that hospitals will often go with the cheapest option making surgeons compete with each other for less. They care a lot about malpractice record, but beyond that pay little attention it seems to qualifications or degree of training.
Hope this helps and definitely happy to keep this convo going.