I purchase most of my stuff from BigBadToystore, they offer $4 flat rate shipping on almost everything.
Retro Mego -might want to look at NECA, they have a Mego series, they have some odd licenses like Bill and Ted, Weird Al, Home Alone. But they also have some Horror Stuff.
Horror-NECA is really the only doing anything worthwhile at your price point
http://www.bigbadtoystore.com/Search?SearchText=neca+horror they have the "Ultimate Series" for $25 or so your getting a highly detailed 7" figure with a slew of accessories, multiple head sculpts and hands to change it up. Jason, Freddy, Leatherface, Evil Dead, Predator, Aliens, Pennywise etc
Street Fighter/KoF - Storm Collectibles is the standard imo a little higher than your price point but great quality, they also have a KoF line coming out soon
http://www.bigbadtoystore.com/Searc...rder=PriceLowToHigh&SearchText=street fighter
Ninja Turtles- depends on the era, the NECA 1/4 scale Movie turtles are pretty much the standard when it comes to likeness. Neca also teased 7" TMNT cartoon Figures at toyFair this year.
http://www.bigbadtoystore.com/Search?SearchText=NECA+turtles
Pics of the cartoon figures
http://news.toyark.com/2018/02/17/t...ge-mutant-ninja-turtles-new-street-dio-286868
Transformers & DBZ - I never collected either so I can't chime in on what's good.
I might sound like i'm a NECA fan boy but for the price point 19.99-24.99 you really can't go wrong. Of course there are much better items out there but then your looking at 1/6 scale figures like Hot Toys or Sideshow but your now in the $200+ price range which can be purchased at Sideshow toy and they offer payment plans
https://www.sideshowtoy.com/ I hope that helps get you started.