Hi @mikhails and thanks for your query. Your project sounds really interesting!
Certainly, if you are collecting data for analysis (regardless if for production or academic use) then you will need to purchase the analytical use licence for which further details can be found @ https://analyticaluse.tobii.com/
For the creation of applications under Linux using Python in conjunction with the 4C, you will need to use the Tobii Pro SDK (https://www.tobiipro.com/product-listing/tobii-pro-sdk/) which support ubuntu and requires a special unlock file to use.
Regarding pricing, if you could kindly PM you private email address I will get one of the Tobii Pro Sales team to contact you promptly.
Thanks for your patience and please let us know if we can provide any further information for your project goals.