If you're looking for the cheapest and "best vps for GSA SER", look no further!
Best VPS For GSA SER
All plans are spam-friendly with unlimited bandwidth. On top of that, fast customer service support. 
Network speed for all plans are 1000 MBPS. Speedtest.net measures all plans to be around the 60-100 MBPs range.
The first plan, for only $11.00, provides 1GB of RAM and 100 GB of HDD. I wouldn't really recommend this plan unless you're just using it for light work. For example, scraping and email blasting. Windows OS is already using about 600mb of RAM, which leaves just 400mb for you to use. You can still run GSA SER with this, but the recommended threads would be around 50.
For the 2nd plan, which is only $20/month, you can run average resource-eating SEO softwares. Like scrapebox, No Hands SEO, Scrapejet, TweetAttacks Pro, Tweet Demon, Pin Blaster, Pin Ranker, Sick Submitter (at 50 threads maximum). If you're using GSA SER, the highest recommended threads is about 100. 
However if you're gonna use Captcha Sniper or Captcha Breaker with GSA SER, then you need to lower the threads by 20%. For example, plan 2 would only run at a maximum of 80 threads with CaptchaSniper on. 
I would highly recommend the 3rd plan that provides 4GB of RAM, 200 GB HDD, with duo core. 
You're able to run Senuke Xcr, Lincorne AIO, SE Demon, Ultimate Demon and many more.
You can run up to 200 threads in GSA Search Engine Ranker. And because it is duo core, it is able to run Captcha Sniper or Captcha Breaker with ease.
Usually running SEO softwares without proxies is okay. But sometimes some webmaster whose site you spammed can file a complain to the VPS' host. They won't suspend your account, but will issue you a warning. So it is still best to run your SEO softwares with proxies.

Regardless, for such a crazy price - it is really value for money! This is, without a doubt, the Best VPS For GSA Search Engine Ranker!
Best VPS For GSA SER