Wether BIAB or 3V, you still need a large enough kettle for a full volume batch, so as long as you have the health or tools to handle lifting a bag or basket, everything you buy for BIAB will remain useful if you decide to go to a larger system. I'm slowly building a 3V keggle based system, but only because I have health issues that demand "accessible brewing". If I could lift a bag, I'd definitely start with that as I'm on a super tight budget too and the larger the system, the more small parts you need that really add the costs up. Take a look at the all-in-ones like the Anvil Foundry, Brewzilla etc.. Otherwise I'd recommend the best kettle (or keggle) that you don't see yourself outgrowing and after the bag or basket, you can start with a pump and recirculating parts and grow from there.