Is there a readily available liquid that's more dense than water and insoluble?
Trichloroethylene is a common chemical solvent that has reasonably low toxicity, it has density ~1.5 g/ml. However, it slowly becomes restricted. Tetrachloroethylene also may be considered. Dichlormethan has reasonably low toxicity, but its BP is too low. I would not use the liquids mentioned without fume hood on regular basis. One-time exposure is probably OK, but repeating exposure may lead to cancer.  Chloroform may be considered, but I recommend to avoid it, it has accumulating liver toxicity. Tetrachloromethane should be avoided, it also has undesired toxicity.

Mercury MAY be considered, it is toxic if one is repeatedly exposed to vapours, but has very low vapour pressure and is reasonably cheap. But it has annoying tendency to produce small drops that are very hard to collect and move into smallest holes and accumulates in the system, so it clearly requires dedicated  workplace. 

Liquids mentioned above are reasonably cheap, so if they are not restricted in your home country, you should be able to allow yourself one. Unfortunately, that's all ideas I got. Well, there are some more, but they either has unreasonable cost, or are too toxic. Bromine, for example, is toxic and, though not mixing with water, partially dissolves in it.