You should definitely check out Amplitude.

disclosure: I work there, but there's no reason you shouldn't try us out if you're looking for an alternative.

Our free plan is for 1 million monthly events: https://amplitude.com/pricing

all the basics you're used to, like Funnels and Retention, plus some other cool stuff like unlimited user timelines (this is extra as part of Mixpanel's People plan)and Event Flows.