There's software only solutions I've tried on my PC, and stuff like GuitarPort (which I've never used) but for the $100 it takes to get GuitarPort, why not just get a regular amp? Especially used... I bought a Carvin SX-100 for like $150 used 5 years ago.
In 2005 in college, I wrote a small article on ReValver Live, which is a program that acts as an amplifier. It was only the demo so it had a beep every 30 seconds. I just listened to a few samples I recorded for the assignment, and it sounds OK. But there is a delay of like 80ms. If you play something really fast with short notes, I remember having trouble with it picking it all up.
In the review of it, I mentioned I had used something called Guitar FX years before and it wasn't nearly as good. Also there is something called Guitar Rig which seems to have hardware now but I think there used to be a software only version.
I'm sure if you bought something nice like Guitar Rig, it would be better than the trial thing I had, but then you're looking at $50-100 (like GuitarPort) and while it would be more flexible, I can't see it sounding anywhere near as good as an amp.