buy one thats done,
have a calculate what you think it will cost then tripple it and you will come close to what its going to set you back,
most workshops will charge at $70 to $100 an hour just for labour and some conversions might take a solid 100 hours,
if its a sigma i'd go for cubes a mivec v6 from a pajero evo or a lexus v8,
if its cheap you want go buick v6 and get ready for a flaming from all the haters