Rare Replay

Here, you need to purchase a total of 50 vehicle upgrades from the shop between races, across all playthroughs of the game - any item that you purchase from the shop will count, including consumables (ammunition, shields, etc.). With consumables typically being the least expensive purchases in the store, purchasing these can be the quickest way to reach the required 50 purchases.

In any case, you'll probably work a long way towards this in the course of your initial playthrough of the game's 24 tracks (if you don't, you'll have a hard time completing the later races), but for the remaining purchases, make a manual save as you're about to purchase an an upgrade (or several). Make the purchases, then reload the save and repeat until you reach the required 50 upgrades.

Note that you cannot use the rewind functionality to work towards the cumulative total.

I'll also include here some details about the available upgrades, which are below. A point to note is that you don't have to purchase these in sequence, so if you an afford to wait before making an upgrade purchase and so 'jump' a tier (or more), you'll save money overall - but you need to make sure that you can still perform well in races in the meantime!

I'd recommend as your first purchase either the black or silver motor, then skinny tyres, scooper tyres and the gold motor. Somewhere along the way, buy at least the buckshot weapon (which makes your opponents drop cash when hit), though I found that you can mostly get by without weapon upgrades. They are of course still nice to have if/when you can afford them, though!

• Motor: Higher upgrades increase your car's speed, with each upgrade being wholly better than the previous one.
  - Standard: your starting motor
  - Red: $2,000
  - Black: $4,000
  - Silver: $8,000
  - Gold: $16,000
  - Hyper: $30,000
  - Mega: $50,000
• Tyres: Higher upgrades tighten up your car's handling, making cornering easier.
  - Standard: your starting tyres
  - Skinny: $2,000
  - Nobblies: $7,000
  - Dynafit: $10,000
  - Scooper: $15,000
• Guns: A variety of weapons that you can use against your opponents, providing an advantage towards winning each race.
  - Buckshot: $2,000 - A forward-firing shot, which causes your opponents to drop money bags when hit. Very useful if you can then manage to collect this money!
  - Missiles: $10,000 - Another forward-firing weapon, this will destroy an opponent's car if it hits them, delaying them for a few seconds until they respawn.
  - Bombs: $12,000 - These are dropped on the track behind your car; if an opponent then collides with a bomb, their car will be destroyed (as with missiles), delaying them for a few seconds until they respawn.
  - Laser: $14,000 - Similar to missiles, but a little more powerful.
  - Freeze: $15,000 - Again this is forward-firing, and in this case will freeze and opponent's car in place for a few seconds.
  - Mega Pulse: $20,000 - Very expensive for what it is, and more useful in the game's multi-player mode than single-player, the Mega Pulse reverses a car's controls.
• Extra: The items in the "extra" category are a range of consumables that you can use to improve your chances in each race.
  - Ammo: $200 - Extra ammunition for your weapon(s), to supplement any picked up from tracks.
  - Shields: $50 - Temporary protection from opponent's weapons.
  - Slicks: $500 - Dropped behind your car, oil slicks cause opponents' cars to spin out if they run through them.
  - Nitro: $1,000 - A brief speed boost, to supplement any picked up from tracks
  - Continue: $5,000+ - A chance to continue your game if you come last in a race. You can completely avoid any need to purchase these if you save at the start of each race (so that you can reload) or just use the infinite continues cheat. The price increases with each successive purchase.