Any feedback is always appreciated, but please keep in mind that the power level of a Traveller card generally does not correspond to its cost.
Not including the final upgrade for each traveller line, I'd say most of the cards are balanced at their "cost." if they were in the supply:
Page -- this would never be bought without it being a traveller. So, this is not priced right.
Treasure Hunter -- looks like costing about 3 works, potentially 2 would work. You might need to slap a +buy on this one to make it work as a 3. The price is close to being right.
Warrior -- This is balanced at 4, but being a traveller makes people tend to upgrade past it, and the final card offers a solution to the incessant trashing. So, if it were in the supply, there might have to be some mechanisms here to prevent the ease of playing a bunch, especially early (other action-trashers are all 5s for this reason). But I'd say it's definitely more than a 3 and less than a 5. The price is at least pretty close to being right.
Hero -- this is a pretty classic 5+. It's similar to Explorer, almost strictly better, but not quite. Think of it like forager/trade route. It would be priced at a 5 in the supply and I wouldn't complain.
maybe a 6 because of the added gain any treasure flexibility. But looks good as is. Hm, on second thought I think a 6 would best. Still, pretty close to the right price.
Peasant -- This is totally priced right, it's a weaker herbalist, but still stronger than a 1. If Herbalist didn't exist, I'd be happy with this as a 2 and buy it without it being a traveller.
Soldier -- Similar to Gladiator, it's a +2 with a possible +3 (in this case, more) if a condition is met. It's about the right cost. 4 might work, but it's definitely a 3 or 4. I'd say 3 is actually the right cost for this if it were in the supply by itself.
Fugitive -- compare to ware house, forum, Inn. 4 again seems about right.
Disciple -- this I am less sure about. I think to be in the supply it would need an anti-self-gaining clause (which is covered right now by it not being in the supply). It could potentially cost 6. 5 might work.
So, almost
all of the power levels of current travelers correspond very well to their cost. The notable exceptions being the end of the line, which I don't think would be easily balanced in the supply at any cost (Champion even more so) at all.
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As far as feedback, I think actually using some of those cost analysis (especially for the beginning of the line) could help. Some of them seem oddly priced. I get that it's a 4 so people can't, under normal circumstances, double up on the traveller line T1 T2. But
why don't you want that to happen? Could you redesign it such that it would be fine to double up T1 T2?
Personally, I am weary of things that say "other players can't do this." Getting rid of choices/strategies makes the game less fun. Matriarch preventing the stealing of artifacts rules out one of the whole fun mechanics of artifacts, stealing it back and forth!
I don't like that getting to Matriarch a few turns before someone could irrevocably change the tide of the game (they get a few artifacts and they are lost forever).
I do think that the four artifacts you included are quite interesting! To be honest, Reliquary seems really under whelming. Trade a card for a copper? This only helps with estates and curses... so it's unlikely to be helpful but it hits every turn. Seems more like a self-hex. Or perhaps that's the point, do you want to have that to power up your matriarch? Ah, I see now. That's pretty cool!!