So you're point about buying a transmission for the B18 is kinda moot. Why not just buy an entire B18B swap for $900? If you want to go LS/VTEC you're going to have to buy either another block or head at some point. If that's your goal, why not buy a B18B block, B16 head, and B18C1 transmission? Don't be in such a rush.
What engine you go with depends on what you want. Do you want low end power or do you want to rev really high to make power? Do you have the $1500 (plus the price of custom pistons) to sleeve and bore a B16 to 1.8l? A B18A/B is 1834.67cc and it'll take an 87mm bore in a B16 to get 1840.67cc. Stroking is also an option, but now that B18B block is looking a lot less expensive isn't it?