The duration and fee of retreatment depends on the extent your teeth has shifted - how much the teeth have moved and how many teeth are involved.
If it is a mild case of relapse, a simple aligner treatment is possible. The fees for this will definitely be lower than a full orthodontic treatment.
However, if the extent of movement is greater, full fixed braces or Invisalign (full) may be required. In such cases, the fee will generally be the same.
To determine the treatment option most suitable for your case, you are recommended to visit your trusted orthodontist so that he/she can carry out a detailed assessment, including taking of x-rays, dental mould (impression) and photographs.
In the event that you decide not to proceed with retreatment, you can visit your orthodontist to make a new set of retainers for you so as to prevent the relapse from worsening.
Best regards,
Dr May Ling Eide