Price: 1.99$
Link: https://www.spigotmc.org/resources/vouchers-a-new-way-of-giving-players-rewards.13654/
It's is also a very good plugin using on many servers.
Price: 10$
Link: https://www.spigotmc.org/resources/supply-crates-envoy-1-7-1-9.12504/
It's very nice and demanded plugin as it is using on many new Gen servers.
Thx