The thing about modern technology is that the cutting edge device is always relatively the same cost as the last cutting edge device. Previous models get cheaper and cheaper as new one come out.
What if you took the same tact?
There are 4 tech levels:
0 - Out dated - cost 10
1 - Standard - cost 50
2 - State of the art - cost 75
3 - Cutting edge - cost 100
As you research a field your research level goes up and you unlock new devices all devices start at level 3 and as your research level in a field increases all devices in that field drop a tech level to a minimum of 0.
You could tie tech levels into production a standard ship yard can build up to level 1 an advanced ship yard up to level 2 and an imperial shipyard (limit 1 per empire) can build up to level 3.
In this way your latest ships can only ever be built in one place you have to do further research to be able to produce them in other locations of build more then one at a time. But even then they can never have the latest tech.