What are the alternatives ? what It would cost

The process of matching buying signals with tailored messages to each persona is quite unique and it has´t been "package" in an all in one plattform , but you could compare it with 3 categories of products
The Buying Intent data providers
Good news is that this can be done at scale. The rest is bad news , starting with the price - above thousands . Then there is the question of .. what are really tracking .. what intent signal is a good indicator AND what action can you take
The Sales Enablement plattforms
This is again an " enterprise play" and anything in the market has a pricing to that segment - that means again thousands a month . On top of the other . And you have not even start to do any matching neither send any message. They of course have other features that might be useful for you .
The sales Outreach tools
Here we have to look into tools for each channel , but before that a note that apply to all- None have the relational database linked to a CRM ( se next point) so the personalisation is just a number of variables that they fetch into their system - name , company , sometimes title, sector and very few more . The best ones ( like Outreach.io and Hubspot have the option to insert Snippets — pre-written text that you can apply to - ALL the recipients of a template. So , not adjusted to any specifics - interest , stage , persona ..
In terms of channel we have THE one and only channel for most providers; email . So any of their super features are limited to a channel that has been so sucessfull that now is totally ineffective ( as in 98% of executives dont ever answer a cold email ) . The prices range for the good ones at a few hundreds a month per user , to very simple but effective in the around 10-15$
So to use other channels , like Linkedin , Slack , Whatsapp , Quora, Medium, Facebook, and a huge long list .. you have add another tool .. almost for each
Anyway each of this specialise tools ..price rage 20- 50$ , have their diferenciator in being specialise in a channel so dont expect any features more advanced than the standard

well , this is not an alternative per se but more a question of how your process look like. You have to have a system to keep track of relationships . But the point some "big and expensive" try to make to justify their big and expensive price tag is that they can be the ONE , the single source of truth . That message works in corporate but is a faulty one. You will never have all you customer data in your CRM. They will be data in islands like Linkedin and many others . But more importantly you dont really want it . About 30% of CRM data get outdated every year. So hell with that. Lets just get fresh data every time . I don´t care what you did last year but what is you views or actions in my subject today. So the best is just get in the channels where you customers are active , find those who matter and enrich their data with the latest social data to act on it
Because thats the real point of a CRM - not to keep records but to do something with the relationship . And that something that happens outside a CRM

So in conclusion , you will spend a few thousands a month per user for a solution which only one dubious advantage - is easier but far less relevant so require less work upfront and you can send in mass to compensate, . So guess what most companies go for ? quantity or quality,

tip - you can use the cheap and leave the intelligence to a solution that work across channels and tools to engage where your customers happens to be . and thats