I got a road bike with 30/40/50 front chainrings and a 12-25 on the back. I am so weak the lowest gear was far too high for me to get up hills (30 divided by 25 = 1.2) so, I "purged" the cassette, rear mech and chain off my MTB and now the setup is 30/40/50 front and 11-32 back. This gave me a lowest gear of 30 divided by 32 = 0.94 which granted is so low I hardly ever use it, but the point to me is that I still have all the gears I used to have anyway, I actually have a higher high gear because of the 11t sprocket. so the last 66% of the gears are the whole range of what the road bike was and the first 33% is lower gearing. The only downside to this is there is no close ratio anymore.
If you had to buy all the parts it wouldn't cost that
much, you just need a long cage rear mech (Alivio is adequate, £30) then a new chain (£12) and a new cassette (check CRC for discounts, I got a SRAM PG850 for £20) so altogether this can be done for about £65.
It was either that or I don't get up hills and I didn't buy a bike to never see any scenery.
FOR SALE: Tinfoil hat (never used).