There are many factors to consider so I can't give you an exaxt answer, for example which part of the game you want to be involved in. If you're interested in playing the collector adventure, all you need is a collector.

In my opinion, farming is a good starting point as it can also open doors to other games. Starting with one farmer would cost around 35 wax only. By doing so, once you harvest your crops, you can also play the collector adventure.

If you're interested in playing the magic adventure, you'll need a magic guild pack. The cheapest way to start the magic adventure is around 25 wax.

the choice of which adventure to start with depends on your strategy. However, none of them are expensive, imo.