The cheap aluminum rads use epoxied tubes. The better ones have soldered tubes.
If you can weld aluminum, by far the cheapest route is to make your own. On average an aluminum rad can be made for less than $200 using excellent quality components.
I get all my cores from here---->
https://howeracing.com/
On a side note;
When it comes to anti freeze, Don't use the green stuff on newer engines because it will screw up the engine seals, and don't use the red stuff with older rads because it reacts with the soldered joints in brass rads.
If you're using a newer engine like an LS and also using the original brass rad, then use the yellow anti-freeze. If I recall, it's propylene glycol.