Product analytics tools like Amplitude and Mixpanel get very expensive at scale. How do companies replace them?

I have been managing multiple domains/sites for my clients since a few years now and I think the easiest and best way to do it in your case would be setting up simple WordPress sites on each one of them and managing them with something like ManageWP(https://managewp.com/) . If they're niche domains, you can monetize them through ads or use them as affiliate sites. Selling them can also be also an option. If you can get the sites to look fairly nice and if they are niche domains, you can sell them on sites like Flippa(https://flippa.com/) . Overall, you have many options. I'd be glad to help you in detail through a call if you want.

Sure, it's correlative for technical reasons, iTunes / AppStore does not provide (yet, might change) a mechanism for that, so 3rd parties have to build their own. I recently discussed with people from Adjust and I was really impressed. HasOffers / MobileAppTracking seems to be a good choice as well.

Top 2 tactics: Existing Users and Industry Influencers. First, leverage the existing user base. Incent referrals with $5 for every new free user they get to sign up and start using PT Engine for a new domain. Second, reach influencers and offer them the same deal when they tweet / post to / email their audiences. Make the offer a 60 day free trial instead of the standard 30 day so that they are providing value to the people they refer as well. This is critical - don't make them feel sleazy, make them feel (and look) like heroes to the connections they share PT Engine with. That's $9k to get 1800 users, leaving you $1k for graphics, referral tracking system, administrative costs. I assume the $10k budget does not include your time - if it does you'll have to reduce the incentive, which will definitely make it less appealing. If you want to dive deep on reaching influencers, schedule a call with me at www.clarity.fm/ryandraving

Try Intercom.io You get visitor level information on how active they are etc.

Here you can find a solution: http://www.lunametrics.com/blog/2015/03/19/eliminating-dumb-ghost-referral-traffic/