@Starooqi ,
@Brictoria gave you very good tips above (to spend the smallest amount on CCU and to leave gaps to fill later, with inserting M2).
If you are going for the very long run I would also bet also on unreleased ships like Vulcan, in addition to inserting more warbonds upgrades from sale in the largest gaps in your chain.
Vulcan will probably jump by 20-30$ (Defender jumped from 200 to 220, Ares jumped from 220 to 250 and Scorpius for 220 to 240).
Start by securing a Hurricane to Vulcan when its on sale (5$).
If Vulcan jumps by 20$ you can save now a Vulcan to Railen CCU (if you have spare credit ie), melt it, and buy it back for 5$ when Vulcan released (if you bet Vulcan will release before the Railen and to have the CCU ready for repurchase at any time).
Then there is another potential bet on the Railen price increase, if Railen only jumps by 20$, and ends at 245$, you can do a Railen to Ares Ion in the future, and then use your Ares to Sentinel warbond CCU.
Of course its all bets, they sometime pay, sometime its a fail :) That's why you need to secure also a safe route like you do, you will save a bit less in the end but at least you are sure you can do the chain. In general, if you have spare store credits, it will cost you nothing to buy and store upgrades in buyback for any potential bets.
In the end, when you can get the cheapest Merchantman (BMM), stop then and wait for BMM price increase, because it will rise in price again before release (I bet 650 this IAE 2022, 700 ILW 2023 and 750 at least IAE 2023 if released then, but more like 800-950 in the end probably). You can get the M2 to BMM warbond upgrade now.
Whatever sale there will be on the Perseus / Polaris / Hammerhead... it wont help as much since if you do it right, you wont have to spend more without sales.
Perseus to Polaris warbond was sold for 25$ before (50$ saving), so if BMM jumps to 650, you need to spend 50$ more $ to get a Polaris (BMM>Perseus 25, Perseus > Polaris 25).
If BMM jumps to 700, you also need to spend 50$ for a Polaris with normal Polaris CCU price (BMM > Polaris 50).
Here I am going for the Perseus route as I have a few Polaris warbond CCU, and will keep 2 for me with those (waiting for BMM at 650). But it would cost me the same without those warbond Polaris CCU, I would just need to wait for BMM to jump at 700$.
If BMM jumps directly at 750 from 600, well :) failed bet. Hopefully during sales, Polaris is usually sold before Alien ships, so if you fear a huge price jump you still have time to secure a CCU (or to buy back if you stored one).
But you have alternative routes then still to save your chain, like using old BMM to Carrack warbond CCU for 10$ (550 to 560), and wait for a Perseus sale and get a Carrack to Perseus then (Perseus probably at 625-635 on sale so 25-35$ cost), and then apply a Polaris warbond CCU on the Perseus (25$). Instead of spending just 50$ with a safe BMM path, at worse you would spend 70$.
If that is the case, I have BMM>Carrack warbond CCU to save your chain and minimize damage ;)
In short always have a plan B