I don't think you're going to hit your price point and get the features you want in one thing without spending a bunch of time building it out of Arduino or Raspberry Pi or the like. Somewhat full circle, back to 87manche's early post, I think you'll be best-off with either a Speeduino (arduino based DIY EFI) derivative or Pi Dash (raspberry pi based) piggyback'd onto your existing computer. Pi Dash would probably be pretty easy to datalog, just leave out the dash part of it and only use the backend for the datalog. If you're not comfy with doing it though, you're either going to have to spend on something ready-made, or spend on a computer geek to set it up for you. Google up Pi Dash for a bit of reading on that, there are guys out there who've more-or-less scienced out the basics, decide if you're OK with that. Both Arduino and Pi can be adapted to just about whatever inputs you have, converting those inputs (like raw tach pulses) into something meaningful is the trick.
Maybe an old smartphone, Torque, and adapt in what signal you have to one of their bluetooth dongles? Not sure if Torque does pre-OBD-2.