at least a couple of companies are selling up to 50 IPs for $1/IP but not sure if dedicated, they don't advertise that. The more reputable companies are selling up to 200 dedicated IPs but their prices are ridiculous.
Almost all of the ones selling $1/ip are on shared hosting, and IF they limit the amount of users on each shared ip you will be ok.
The issues start when they sell the same ip over and over to too many clients, then you start to get community creep and if your in a good community it will bleed rep to you, if your in a bad community no amount of seo will help.
I have been doing SEO and providing seo services for many years, and you have no idea how something like this affects your overall sites ranking ( among many other factors)