Use a Hardcore elevator, not a survival vote. The mode stays Hardcore, consumables are off, and the ready check replaces the difficulty vote. Starting cash is $900, or $1,000 with the group bonus.
Gem prices at level 50
| Tower | Gems | Robux alternative |
|---|---|---|
| Brawler | 1,250 | None listed |
| Necromancer | 2,250 | None listed |
| Accelerator | 2,500 | None listed |
| Engineer | 4,500 | 1,690 |
| Hacker | 5,500 | 2,249 |
Buy from the top of that table if Gems are the limit. Engineer is not a coin tower, and a lower Robux number that still gets repeated does not match this 1,690 price.
Engineer can draw an orange circle in addition to its white range. Place it so the path you care about is inside the circle that actually fires. Sentries are part of this tower; they are not the removed Sentry tower from the unavailable list.
Hardcore is also where Gem income for this row comes from. Creator videos quote hourly gem figures such as a few hundred per hour. Those are their routes and their patches, not a reward printed on the mode page. If a route asks you to skip every wave instantly, you still have to survive the stacked enemies.
Polluted Wasteland II is the other level 50 door. It starts at $850 and its triumph unlocks Saboteur for coins, which Hardcore gems do not replace.