This is my budget / beginner Lanka build for Eidolon hunting. It's meant for those who want to start contributing damage-wise during hunts but don't have the forma/mods/endo/rivens yet for the one-shot builds. You will eventually outgrow this, but it should put you on the right path. Requires a potato & only 1 forma. If you need to buy either of the two rare mods, the plat prices for them are very reasonable if you use Warframe Market. Damage is better & endo costs are lower than the other zero- and one-forma Eidolon builds I've seen.

This build isn't frame-specific, but I've used it to successfully solo teralysts with [Rhino] (Roar, Iron Skin and energy pads). It can be a pain in the butt, though, since you're having to take down the shields, hit the synovias, deal with the vomvalysts and manage the lures all by yourself. Patience is definitely a virtue if you go it alone. Much easier with help, even if it's just dropping into a random pub squad whose only contribution is assisting with the shields & vomvalysts.

Happy hunting, Tenno!