Widows. Medically significant, globally recognized, and legally restricted in more jurisdictions than anything else we track.
L. mactans, L. hesperus and L. geometricus are the common ones. Small, web-bound, sedentary, and not aggressive in any meaningful sense, though the venom is real and antivenom exists for a reason. Husbandry is trivial: a container, an anchor point, and small prey.
Check your local law before ordering. Several US states and many countries restrict or prohibit possession, and vendors do not always screen. Prices are very low because they breed easily and produce large egg sacs, which means the legal risk, not the cost, is the thing to actually think about here.