I'm sorry to hear that some of your gear and especially your son and his family's home got caught in the flooding!
The Sigma 50-500mm is a pretty old design now, though it's still in production (but only the later version with OS). It might be that they'd apply the discount to a newer design such as one of their 150-600mm. Sigma offers two versions of 150-600mm: A less expensive "C" or "consumer" version and a more expensive, better built and optical "S" or "sports). They also have their even newer, smaller 100-400mm "C". All of the currently available 50-500, 100-400 and 150-600 have fast "HSM" focus drive and "OS" stabilization. They also made a 50-150mm f/2.8 at one time, but I don't think they still do. It was a "crop only" lens, while all the others are usable on both full frame and crop cameras. (Note: I'm not a fan of Sigma's 100-400mm, because it doesn't come with or even have option to fit a tripod mounting ring, which I consider necessary on a lens of this type. Tamron has also recently introduced a 100-400mm, too, and theirs doesn't come with but they offer an optional t'pod ring. My Canon 100-400mm II came with a t'pod ring and I often use it!)
Compare cost (new), weight and size:
- Sigma 50-500mm f/4.5-6.3 DG APO OS HSM is selling for $1659, weighs 4.33 lb. & uses 95mm filters
- Sigma 150-600mm f/5-6.3 DG OS HSM "C" is selling for $989, weighs 4.3 lb. & uses 95mm filters (similar size & weight).
- Sigma 150-600mm f/5-6.3 DG OS HSM "S" is selling for $1799, weighs 6.3 lb. & uses 105mm filters (more expensive, bigger & heavier)
- Sigma 100-400mm f/5-6.3 DG OS HSM "C" is selling for $799, weighs 2.55 lb. & uses 67mm filters
Compare to Canon 100-400mm II f/4.5-5.6L IS USM "II" that costs $2049, weighs 3.5 lb. & uses 77mm filters.
Or to Canon 70-200mm f/2.8 IS USM "II" that costs $1949, weighs 3.28 lb. & uses 77mm filters.
If you emailed "Tameron", I'm not surprised you haven't heard back from them. The company's name is "Tamron"... no "e". If someone named Tameron got your email, he (or she?) is probably wondering what a 150-600 is.
Tamron SP 150-600mm f/5-6.3 Di (full frame or crop) VC USD "G2" is the current and improved version, on sale right now after rebate for $1299, 4.42 lb, 95mm filters. The older (not "G2") version is still available new and deeply discounted right now to $799, weighs 4.3 lb. & uses 95mm filters.
I'm also not familiar with a "Canon 100-200 2.8". They made a
100-200mm f/4.5 quite a few years ago... as well as a long discontinued 80-
200mm f/2.8L and three different 70-
200mm f/2.8L (a non-IS and an IS "II" versions are currently in production, while another, earlier IS version was discontinued several years ago). If it's one of the L-series, I'm not surprised to hear it fared a bit better, since those are typically better sealed than many other lenses. They're not "water proof" by any means, but more "weather resistant". An L-series is probably worth fixing and should be cleaned ASAP. Fungus can etch glass or coatings on elements, ruining them. I don't know, but Canon also might offer some relief for flood victims, too.
Several previous response suggested checking with your homeowners insurance, and that's probably a good idea. Your gear might be covered in part, even when it's not in your home.