Full preparation to attend a party of 30 people, he is responsible for buying drinks. There are three specifications of cola drinks in the supermarket, namely 600ml (small bottle), 1.5 liters (medium bottle), 2.5 liters (large bottle), the prices are 2.5 yuan, 4.5 yuan, 6.5 yuan, and the cheapest group of plastic Cups (40 pieces) cost 5 yuan. Manman thought: medium bottles and large bottles seem to be more cost-effective, but it is impossible for one person to drink so much, so you need to buy cups; if you don’t buy cups, everyone must have a bottle. Pour drinks, and the large or medium bottles have to be shared, which means that each person must have a small bottle. According to previous experience, most people are not enough after drinking a small bottle, so Manman decided On average, each person should have more than 800 milliliters. How should I buy it to minimize the cost? What is the minimum cost?
满满准备参加一次30个人的聚会，他负责买饮料．超市有三种规格的可乐饮料，分别是600毫升(小瓶装)、1.5升(中瓶装)、2.5升(大瓶装)，价格分别是2.5元、4.5元、6.5元，而最便宜的一组塑料杯(40个)需要5元，满满心里想：中瓶和大瓶的好像更划得来，但是不可能一个人喝那么多，那就要买杯子；如果不买杯子，则每人都要有瓶子来倒饮料，而大瓶或者中瓶的要分着喝，那意味着每人要有一瓶小瓶装的，按照以前的经验，绝大部分人喝完一瓶小瓶装的以后还不够，于是满满决定平均每人要有800毫升以上，请问应该如何购买才能使花费最少？最少需要花费多少钱呢？
<gadget id="calculator">65 + 5</gadget>
<output>70</output>

<result>70</result>