If you want affordable, Jogaca is the man. He rebuilds OEM shocks and valves/springs them to your weight and riding style. He will be able to supply the front shocks, unless you can find some yfz 450s that will fit it. Your rear shock is probably suitable for a rebuild and is a fully adjustable piggyback, so you can save some money there.
All said and done, you can have your entire setup rebuilt and valve/sprung for probably around $750 or so.
Or you can get some Elkas for twice as much. Will the Elkas perform better? Probably. Just have to weigh your options.
IMO a $1500 set of Elkas on a 660 is probably a waste, and you won't see much benefit over rebuilt OEM.