I think your friend's sand burrowers were likely Bobtailed squid. They have a very short natural lifespan (about 8 months I think) and we only see them occasionally on TONMO. I know there is a species from Hawaii but believe there are others as well.
The Octopus mercatoris is the smallest octopus we see. It is a nocturnal species from the Caribbean and has an arm length of 4-5 inches (so an 8 to 10 inch arm span). A 30 gallon aquarim with lots of hiding places makes a nice home for these little guys but the major disappointement is that they are rarely seen since they are both nocturnal and the least active of the animals we keep.
Sepia bandensis is almost the only cuttlefish available in the US (imported, usually as eggs, from the Philippines). This cuttle will grow to about 6" and even if you only keep one, there are issues with them hurting themselves by bumping into the glass if the tank is too small. Additionally, care of hatchlings is very expensive for the first month or two as they need small live prey (mysis shrimp being the proven successul aquarium food). Not only is it hard to keep mysis alive (expect to reorder frequently) but you will need an additional food aquarium form them.
Care for either will be significantly different than keeping a pico reef. We firmly recommend cycling a tank for a minimum of three months, continually building the bacteria, before introducing an animal. Their food will need to be some form of crustacean and just the hidden shells and waste can easily foul the water. You will need to add a skimmer to the set-up (especially important in a smaller tank) to remove ink (in addition to adding to the water quality by removing protein). For an octopus, you will need to design a secure top to prevent unwanted exit. Please visit our Tank Talk section for some ideas on set up and our journals for both care and tank arrangements.