So, it seems to me like your primary target here is the suppliers marketing budget. The line of thought is that if marketing goes away, then stuff gets cheaper.
So your plan is to alert sellers directly when a product is for sale. So if 1 million products came up for sale today, I'd get a million emails? That doesn't seem workable, but maybe I've missed something?
No cost to buyers? Means that sellers will pay to support this service? Which presumably comes out of their marketing budget? But (I'm guessing) they only pay for goods actually sold (so should relist their entire inventory every day?)
Edit - I reread - no cost to sellers. So (small?) cost to buyers, like um, an auction premium. Which the buyer should factor in...? Seller still going to relist though...
If I have an innovative product, how will I reach new people? People like my mom who don't even know that an Automated Back Scratcher 2000 exists? Perhaps by Marketing it?
All of this is predicted on suppliers using a "cost plus" pricing approach? As distinct from a "market price" approach? If my competitors are selling at $100, including a $75 marketing cost, then I should sell "direct" (well, not really direct, but through your site with presumably lower charges) at $25? Why would I do that? Why wouldn't I sell at say $99?
How is your site not just eBay?
I'm sure you've thought this through, and can illuminate me. I suspect an FAQ on your web page might help answer this too...