BR,
I fully understand your problems with the cashflow, I had to do everything over a long period of time when I first started machining at home, and it took many years to obtain the machines and tooling I wanted. So you must go with your heart and wallet with that decision, and don't be forced into making the decision, you are the only one who knows what you can afford to buy without stretching yourself. We are here to show you what is available.
The tailstock bit was only a suggestion, but as you expand your machining facilities, you would just buy the holder to fit your new machinery, and use your already purchased collets. That might be a long way down the line yet, but a little planning now can save a lot of pennies in the long run. There are lots of new ways being thought up how to use these collets, and they mostly seem to be based around the 32 size, which looks like it is going to become the accepted standard size for general machining.
There is no difference in the grip, as the pressure is applied by the nut, and that is a standard throughout the range of holders. The only difference is the type of nut, I use a ballraced one, and that imparts a lot more pressure because it overcomes the friction between the nut and collet.
John