I've made this
For about $6 total. It's a simple impedance matcher that allows you to use your own sound card. If you feel like tinkering, you can't really get cheaper than this. The quality is okay-ish, and could certainly be improved by fiddling with the capacitance a bit and adding more shielding.
For anything more serious, I'm using a modelling unit; you can buy really nice ones with USB for under $50 nowadays, so it might be worth to save up a bit and go for something like that, used if need be; older models can still work nicely and you can get them for cheap if say a knob is broken, which won't impact your desired use at all.
Here's the forum thread I used as an inspiration.
I used slightly modified1 version of this:
Attribution for the design and picture goes to the DIYStompboxes forum users.
1: I used 2n3819 and added the additional 10kOhm at the end. I don't think it really matters, but I've put 100kOhm at the front (before the transistor, it varied from circuit to circuit). I've attached about 4" cable with male 3.5mm jack from one side, and the 1/4" jack socket at the other.