In this work, inexpensive manufacturing of unibody transparent mesofluidic platforms for pressure-driven Lab-On-a-Valve (LOV) methodologies is accomplished via rapid one-step 3D prototyping from digital models by user-friendly freeware. Multichannel architecture having 800-1800 μm cross-sectional features with unconventional 3D conduit structures and integrating optical and electrochemical detection facilities is for the first time reported. User-defined flow-programming capitalizing upon software control for automatic liquid handling is synergistically combined with additive manufacturing based on stereolithographic 3D printing so as to launch the so-called fourth generation of microflow analysis (3D-μFIA). Using an affordable consumer-grade 3D printer dedicated LOV platforms are 3D printed at will and prints are characterized in terms of solvent compatibility, optical and mechanical properties, and sorption of inorganic and organic species to prospect potentialities for the unfettered choice of chemistries. The unique versatility of the 3D-printed LOV device that is attached to a multiposition rotary valve as a central design unit is demonstrated by (i) online handling of biological materials followed by on-chip photometric detection, (ii) flow-through bioaccessibility tests in exposome studies of contaminated soils with miniaturized voltammetric detection, (iii) online phospholipid removal by TiO2-incorporated microextraction approaches using on-chip disposable sorbents, and (iv) automatic dynamic permeation tests mimicking transdermal measurements in Franz-cell configurations. A multipurpose LOV fluidic platform can be fabricated for less than 11 Euros.