But the $70M only buys the R&D not the bombs that's 1.1B$ more...... ie 165-225 M£ ............and developing the bomb earlier would likely be more expensive rather than less due to having to do more R&D (ok you could with total hindsight only use one of the many OTL routes)?
Yes, exactly. The R&D is not too much pain but the rest of the nuclear program is fabulously expensive and this still excludes the delivery system. If it's any help, the hook to hold the bomb in a B-29 came from the Lancaster.