Archival and cheap don't mix.

It used to be Giclee Iris prints were the way to go but now just find a printer who does:
Lambda or Lightjet prints on Fuji Crystal Archive paper (for photographic reproductions)
or
Pigment based inkjet prints usually with at least a 720dpi printhead capability (for fine art you want to push over 1800 actual - be careful of 'perceived' numbers). These are you paper poster prints. If aqueous, have them overlammed or seal coated. If solvent, not always necessary.

There are not many online places that will do this properly. At least, I don't know of any.

Are these posters you designed? No one will copy existing for you.

Yes, they are 2 of my photographs that I want to print and frame. I had them printed once before but they faded badly within a year.

If they are photographs, have them (or the negatives) professionally scanned at a lab that also has a lambda or lightjet printer. Note I didn't say bring your digital file. Be sure if the file is digital, the resolution is there. 200dpi at final size minimum for fine art prints. Usually 400dpi is used.

Make sure they use the Fuji Crystal Archive. Have it overlammed with a UV inhibitor lam too before framing. I'd suggest a luster lam if you are putting it under glass. Labs are used to dealing with one-offs so two images shouldn't be a problem.

If you really want them to last, have them mounted second surface to a non-glare plexi (if you really want to go all out ask for OP-3 plexi). With the photos mounted in this way, air can't get to them so it slows oxidation. They still can't withstand years of direct sunlight but will last a loooong time in normal ambient room light (Wilhem tests at 40 years unprotected under glass at 12 hours under 400Lux before you get any color shifting).

Some of the pigment inkjets are rated longer (up to 200 years but I don't believe it) and are considered the new giclee process. Depends on the inkset and the substrate. With cost appropriately scaled.

Dye based pigments are what you probably had. They only last about 6 months before fading visibly and totally go off the deep end in a year. There is a reason they are so cheap.

Nothing I said above is cheap.