Fix bridges scripts to test Rococo <> Westend bridge locally (#2752)

I think I broke it in
https://github.com/paritytech/polkadot-sdk/pull/2139 - fees has
increased and amounts that we send are no longer enough to cover fees.
Also changed a consts (test + 33%) using latest weights.

---------

Co-authored-by: Branislav Kontur <[email protected]>