I don’t quite understand the cluster part of it, does it mean spending that much monthly as in 870 dollars or am I missing something?
NT$870 translates to '870 New Taiwan Dollars'.
USD wise, it's saying USD $29.99. Also, you only pay this $30 just ONCE, and you permanently have the game. You shouldn't feel worried about the NT $870; if you want more understanding, just paste into google 'NT $870 to USD'
After you pay the amount, you can choose to continue to support, or end the subscription. Continuing to support helps eccma continue to make updates by donating that amount monthly, but either way, you will have the game forever from the single purchase.
Also, I believe Cluster is the only place you can purchase it currently. Happy to help if you have any other questions.