Valve stem seals, blue smoke on startup, worse when cold.
Under acceleration, piston ring bypass
Fouling plugs, piston rings, valve stems or massively overfueling. Smell fuel when changing oil? [bore wash, piston ring damage, dead engine]
Cheapest option Is probably to get good 2nd hand engine. Find someone you trust to change it.
If you want to know whats wrong you need a compression test to check piston ring seal, if thats ok a leakdown test will check valve seal etc
[disclaimer : This is an internet diagnosis and is not worth the web page its written on]