Chak, paid $50.00 for mine. The question was "What is your go-to cheapie cartridge?", not what cheapie cartridge should I buy, or what is available used. I can only answer the question that is asked, not the one that I imagine in my mind is being asked.
That’s my go-to cheapie. My second choice is my Supex SD900 Super E+.
Tony, having owned quite a few 103 and two 103Rs, I find the 103R to be focused on the upper midrange and low treble, and find the 103 to be darker, but much better balanced overall. These are simply matters of taste and one man’s bright is another man’s detailed.
I’m with Chak on arm choice. The greater the effective mass of the arm the better the 103 series sounds to me, well, except my 103D, which is an entirely different animal and prefers a medium mass arm.