£10 or so, its not voodoo, just fit the new spoke making sure it goes over/under the right spokes, keep turning the nipple untill the rim is aproximately straight. If it wont go perfectly straight get an elastic band and a pen, position it on your chainstay so that it just contacts the rim at its most buckled (make sure your looking at the buckle not the other 90% of the rim) then loosen/tighten the pair of spokes at its center 1/4 turn untill its straight. If you run out of tension in a spoke, go round the whole rim and add 1/4 turn to each spoke.
Repeat untill the wheel is straight.
Use the same method to check for vertical movement in the rim, but tighten/loosen both the spokes to correct high spots or flat spots (flat spots are almsot impossible to fix as usualy the rim is deformed not a result of spoke tension).
De-stress the spokes by restign the axle on a block of wood and applying your bodyweight accross opposite pairs of spokes so you can feel the wheel flex as the spokes on the far side slacken.
Repeatt he whole proces untill the wheel is as straight as you deem nececary (1mm is usualy fine, don’t wory about the rim where the valve hole is or where the join is (usualy opposite), it’ll walywas be slightly wobbly here.