If we're not counting major bits of kit like my Brason Strat, I reckon it was one of those tiny Korg Ampworks amp modellers.
So much easier than messing with a full size amp.
In hindsight, they do leave a bit of "noise" on the recordings, which I have to take care of later but it has been "instrumental" in helping me record my stuff. And I think it was less than £20.

IAn