Really tough to beat the Radial DIs---but you did say $50 and under:
If you need features like pads/speaker tapping, ground lifts, link/through jacks, HF filters, limiters, phase reverse, and/or two-channels, the best deals (active or passive) for $50 and under would be the ART lines of DIs. I've used an ART DPDB for years between my floor modelers and amps/FOH and it's worked great for live gigs (my Radial units stay home for the critical stuff). I didn't really like the PDB for instrument-->recorder (i.e., no external preamp in the signal chain).
I picked up a Behri active DI to try it out but (1) the battery is an absolute monster to install/change and (2) I found it to introduce hiss. The ART active and passive units are noticeably more noise-free.
You could always pick up a version of the ART Tube MP. It can be a nice instrument DI. The basic version sells for $30 at MF, and there are some other variations of the MP available for under $50. It also serves as a mic pre with phantom power and phase reverse.
If you wait to buy a Radial DI, you'll only have to buy once.
Paj
8^)