Learn to weld.
I hadn't done any before but bought a mig for £150 and as mentioned above watched lots of how to's and practiced, get some offcuts from a welders/metal fabricators, ive since done the whole underneath from the headlamp boxes straight through to the boot floor no problem (made every piece myself except the rear outer arches) pre made parts are cheap enough, these guys do good parts:
Discovery 1 Parts - YRM Metal Solutions
All you need from start to finish is an angle grinder and disks, the welder with wire and gas, some anti rust treatment (fertan) some seam sealer, some red oxide and some underseal (tetra shultz).
And your landy can live FOREVER!