Stardust and candy can be hard to come by. While Pokemon like Mewtwo and Dialga are powerful monsters that do tons of damage, they’re not exactly accessible. They seem even less accessible when you realize you need a team of 6 for raids, plus extras, plus different moves for PvP.
Okay, technically Dragonite isn’t a cheap Pokemon to power up. But when it comes to dragon types, it’s by far the most common. Dratini is the most likely to spawn in events as well. If you live in the Northern Hemisphere, there’s a chance you’ll find them in the wild, regardless of events.
That being said, Dragonite still holds its own. It doesn’t deal as much damage as big-name Rayquaza, but Dragonite actually has more uses! Not only is Dragonite a bulky dragon for PvP, but it still does enough damage to be useful in raids, especially in the last slot. You can also happily throw Dragonite in gyms. It’s no Blissey but at least it’s bulky and it’ll throw off the Machamps people normally use to clear out gyms.
Machamp is just too much of a good all-rounder to be skipped. Fighting is a strong, attacking type, and there’s a good number of bosses weak to it. Not only does Machamp beat up rock types, but it does a number on otherwise-tanky Steel types as well. While yes, Conkuldurr and Lucario are slightly better, those are both restricted to raids and eggs, making them VERY hard to get candy for. At least Machop is common from Team Rocket Grunts and 5km eggs when it’s not available in the wild.
Even in PvP, while Machamp isn’t the greatest (mostly because of all the fairy types), it does have two good coverage moves, as well as one of the best fast moves available, Counter.
Bonus points for Machamp, you can trade Machops and Machokes. Even if they don’t become lucky, they then cost 0 candies to evolve into Machamps! So you can use those 100 candies to power up a Machamp instead.
Gengar’s here for the same reason Machamp is. It’s fairly common, it had a community day and it has lots of good moves. But, more importantly, Gengar has the same cheaper evolution costs Machamp has. If you trade a Gastly or Haunter, the cost to evolve that Haunter into a Gengar is zero.
Gengar’s only real downsides are that it’s squishy and it has Poison as a secondary type. This means it takes Super Effective damage against Psychic types. But at least Gengar dishes out huge amounts of damage before it faints.
The Eeveelutions definitely aren’t the best in class. But all the eeveelutions, aside from Umbreon (and maybe Espeon) are great budget Pokemon when it comes to raids and grunts. On the flip side, Umbreon is an amazing choice for PvP, even if its only coverage move is Last Resort. Glaceon in particular is a good backup choice if you don’t have Mamoswine or Galarian Darmanitan, since it has pretty much the same moves.
Eevee is always a common spawn, but also appears frequently in events. Its three Kanto evolutions also have a chance of spawning in the wild. This makes it easy to get candies for.
At just 50 candy to evolve and weather-boosted in sunny weather, Excadrill is a bargain of a Pokemon. This little armoured drilling guy packs enough power to stand at the top of the class when it comes to ground types. While Excadrill lacks the bulk that other ground types have, it makes up for it with an attack stat and move set that put it on par with Groudon. It’s also not far behind Therian Landorus.
But unlike those two, Drillbur, Excadrill’s basic evolution, has been available pretty much permanently, and has been around in both Season of Celebration and Season of Legends. And since it’s weather-boosted in sunny weather, you can quite easily get high CP ones too!
Excadrill also works as a backup steel type. Unfortunately, like pretty much every other steel type, it pales in comparison to Metagross.
There are other cheap Pokemon that you can power up, and really, anything that has a community day is a good choice. But these Pokemon give you the most bang for your buck.