Yes, the free money readily flows by the tens of millions for private companies in Texas, but not when it comes to protecting people's lives.
In my mind the failure in the system wasn't in the lack of warning sirens of an impending flash flood, it was allowing the construction of structures meant for housing sleeping children in an area known for flash floods.
There's some responsibility of the loss of life on any government agency that allowed for habitable structures in a flood plain. Then there is some responsibility on those that did the construction, both the people that laid out the buildings at the camp and those that did the construction.
There's means to alert people of an oncoming flood besides sirens. There's cell phone alerts, but apparently this camp didn't have reliable cell phone service. There's weather radio, which I suspect was in place as the National Weather Service appears to do a decent job of having transmitter sites that will cover the USA. Did they have a landline phone? I would hope so as I'd believe it irresponsible to not have some means to contact the camp, or for the camp to contact others, should there be any kind of emergency.
Many times in remote locations, where sirens would be impractical, there's plans for police patrol cars (and potentially other first responder vehicles like firetrucks and ambulances) to drive to known locations of weather warnings to warn people by sirens and public announcement speakers. The problem with that idea is just how remote this camp was and the size of the area at risk, there was simply not enough first responder staff and vehicles to warn everyone in time.
I grew up on a dairy farm where we'd not be able to hear a weather warning siren. In such cases it was on us to track the weather by listening to the radio or watching TV. I don't recall if weather radio was an option at the time but I do know that we could receive a number of AM, FM, and TV stations. As remote as this summer camp might be I suspect that they were in range of some AM radio station that would provide a weather alert, and it is because of how well AM radio stations blanket the nation with EAS coverage that Congress decided to mandate all new cars to have an AM radio reciever. Again the NWS weather radio network likely covers the area, and there's radios that will listen for the alerts on all NWS weather frequencies and will sound an alarm even when "off" (as in powered but not providing the audible weather announcement) which are readily available and not all that expensive. I have such a weather alert radio in the form of a bedside clock radio.
Last but not least is satellite internet and phone service, including the text only satellite cellular service that's been advertised for newer Apple and Android phones, which should be able to provide a link to most anywhere on the planet to get weather alerts.
My point is that there's far more to the loss of life than just a lack of sirens. The buildings should not have been in an area known to flood, and there's plenty of options for people at the camp to have a connection to the outside world to receive weather warnings. I'm thinking at a minimum they had to have a landline phone or some kind of radio for the summer camp to receive warnings in time to get children at the camp to higher ground.
If this is a matter of insufficient funds to the local government then attracting businesses with some kind of loan, tax break, or subsidy would not only payback whatever funds were used to get the business in the area but also provide funds long term in the form of property taxes and more jobs in the area for income taxes to pay for infrastructure projects like weather sirens or whatever to better warn people of severe weather. I doubt any local or state government would provide these sweet deals in the form of government funds if they could not expect a return on that investment long term, doing otherwise is just bad accounting.
I realize that was a rather long post but I wanted to cover all the ways that the summer camps in Texas should have been able to get a warning on the incoming flood besides sirens with enough time to get to higher ground.