I think you are being taken for a ride. No pun intended. You don't have to listen to the mechanics telling you tall tales. You can do all the fact finding yourself.
First thing you need to know is that 9 times out of ten what you call "bubbling" (correct term is wobbling) at about 80km/h is balance related and the same phenomenon at 100 - 120 km/h is tire/rim out of round related.
Next you need to use the process of elimination to zero in on the problem rather than throwing your money at the car hoping you will get the problem resolved. Begin with the front rims. Go down to your local tire guy who has a balancing machine. Put the tire on the machine and tell him the just spin it for you - not balance it. While the wheel is spinning, look at the tire and the rim. Look at the movement of both; what you are looking for is wobbling of either the rim or the tire. You need to look at both sides of the rim (outer and inner) to make sure there is no wobbling at all. If the rim is not running true, obviously the rim is at fault and if the tire is not running true, then ....... You get the picture. Oh yes, while the wheel in on the machine, look at is the threads (the part that contacts the road). If you see any appreciable bounce at the threads, tire needs to be replaced. Very minor bounce on the treads is acceptable.
Next repeat the same for the rear tires.
My guess is that you will find the rims running true while there may be some wobbling on the tire.
The above work will cost in the range of 500/-. That is a lot better than spending tens of thousands which may not have been required. From this point you can draw your own conclusions and go from there
