Extruded t-slot is what you are trying to buy. Personally, these "maker" t-slot profiles, while interesting, always turn out to be relatively expensive, though they do have certain qualities that make them nice. They also tend to fall into a category of where you are always wondering where to buy the stuff, because it seems vendors are always running out, or dropping the product, etc. I tend to wonder how long they will last in the market.
If you can live with slightly larger stuff - then you might look into one of the "standard" t-slot profile systems, like 80/20, Fastenal, Futura, etc.
These guys (especially 80/20) are industry standards, but their smallest profiles tend to be slightly larger than the "maker profiles" you see out there. This can be a plus, though, as it will lend rigidity to your projects. Furthermore, since many of these have been on the market for many years (or decades), you can find a ton of 3rd party stuff as well for many of them. Also, ordinary hardware will (in general) work ok with many of them.
Another option, that might be cheaper - if you can live with the heavier weight - is steel perforated extrusions (Unistrut is a well known brand). Many times, you can pick the stuff up at most hardware stores. Typically, you can easily buy it from metal suppliers locally as well. That, and some nice bolts, plus a hacksaw or other cutter - then using gridbeam construction - you can make some really nice things, that will be really solid. It will be pretty heavy stuff - but then again, you can easily attach other things to it, as well as easily weld to it (without needing a TIG welder, or a MIG with a spool-gun).