if it was my money id build and boost the KA.

rough estimate of ka24det setup:
spare ka24de - $500
worked block, balanced rotating assembly, forged internals, high volume oil pump - $1600
tubular turbo manifold, 3" downpipe, 3" IC piping - $1500
valve job, p&p, turbo grind cams, upgraded valvetrain components - $1500
generic turbo - $1000
FMIC - $800
sell off your old KA - neg. $500

= $6400

rough estimate ka24de N20 setup:
spare ka24de - $500
worked block, balanced rotating assembly, forged internals, high volume oil pump - $1600
valve job, p&p, N20 specific grind cams, upgraded valvetrain components - $1500
NX Dual Stage N20 system - $1500
sell off old ka - neg. $500

= $4600

Price I've been quoted for blacktop SR20DET into S13 (drop off / pick up):

around $4,000-$5,000.
add tuning, upgraded manifold, FMIC, 3" downpipe, cams... around $2700

so that takes your price of the SR to about $7,000 - $8,000 for an unbuilt motor. also you can find KAs all over the place. youre gonna have to wait a while to have your SR show up on your doorstep with a banged up oil pan because it was sent in seram wrap from malaysia ( ) i dunno to me it just makes more sense to build and boost the KA but look at greaser hes running 10s on an SR...