These 493 slots let you buy the bonus round instead of waiting for scatters to trigger it. A standard buy usually costs around 80x to 100x your bet. Some games offer more than one option, such as Hacksaw's cheaper BonusHunt FeatureSpins or Pragmatic's 500x Super Free Spins.
Buying a bonus doesn't improve the odds. The price is set so the return is about the same as normal play, and since most of these slots are high or extreme volatility, many bought bonuses pay back less than they cost. Set a budget before using them.
Hacksaw Gaming has the most bonus buy games here (155), followed by Pragmatic Play (169) and NoLimit City (106). Tombstone Slaughter: El Gordo's Revenge has the highest listed max win at 500,000x. Bonus buys aren't available in every country and are not allowed in the UK.