How much of an increase in budget (either in Billions of USD or a percentage of our GDP) would be needed to increase the size of the entire force from 161-163 ships in total to a force of about 200-250 ships?
More than budget, what's necessary is optimization. For example, why limit the construction of DDGs to just one yard? Why not bring yards like L&T Kattupalli into the mix? At any given day Kattupalli is a far more efficient yard than any DPSU.
Additionally, the DPSUs themselves should be divested and turned into Privately-held & managed companies. Air India can prove as a good model for how to go about doing that process.
Unless such optimizations are done, it would be quite pointless to increase budgets.
In most areas we are just replacing old ships, not adding new ones(exception:Frigates).
That's what the numbers I've written show.
NGD will be new addition. Destroyer fleet will grow because of them.
For the longest time IN had 8 destroyers (5 Rajputs & 3 Delhis).
For foreseeable future this will become 10 (3 delhi, 3 kolkata, 4 vizag).
Post-2030, it will become 12-13.
But of course there are other considerations too besides numbers...for example a P-17A frigate is far far superior in terms of capability & seakeeping to any Delhi or Rajput.
Personally, I wish we abandon the Delhi lineage with P-15B. A clean sheet NGD for carrier task force A2/AD while increasing numbers of P-17A to 14 or so by on-boarding L&T Kattupalli as a 3rd shipyard building the type.
Unless there's going to be a serious shift in DDG-FFG roles (along with shift toward MT30), the P17A itself is the perfect baseline platform. Incremental improvements to that design via P17B, C should keep us in good shape till 2050 even.
We should probably tap into the IEP solution being developed for the US Navy's Constellation-class FFG (which uses LM2500) in that case.