The motor is often the cheapest part of a 4age conversion.
The trouble these days is finding all of the ae71 bits you need to do the conversion in a ke70.
T50gbox, pedal box, cross members, tailshaft to suit your chosen diff. Ae86drivingclub is the place to get all these bits.
When I did my conversion like 6yrs ago I refreshed the top half of the engine and bought everything new that I could. Clutch, clutch master and slave cylinders, water pump, gaskets, seals. A custom made proper exhaust. In the end it was almost $3k but it gave great service for yrs. Do it once do it properly.
Also I've seen multiple ae92 sx or csx cars for sale for like 600bucks lately. 1000bucks for just the engine is a bit steap I think. Small port 4age is a great choice but you do need to deal with the intake manifold. Cut and shut is the easiest but it's cast aluminium so not the easiest to weld. Nothing a good welder cant do though.
A 4age ke70 is very fun. I miss mine:/