**For your budget, I’d photograph every signature now, then preserve the signed sections of peel by drying them.** Expect the peel to shrink, curl and darken; preserving the orange’s original appearance is much harder.

I don’t see the picture attached, so this assumes you can remove the signed peel in reasonably large pieces.

Here’s the approach I’d try:

1. **Photograph all sides clearly**, with close-ups of each signature. Keep backup copies.
2. **Practise on another orange**, ideally marked with the same type of pen. This will show how drying affects the ink and peel.
3. **Cut around the signatures and gently remove those sections.** Remove attached fruit flesh from the inside, keeping juice and your fingers away from the ink. Avoid washing the signed surface.
4. **Dry the pieces with steady airflow**, on a clean mesh rack in a dry room. A small fan can help. Orange peel can be dried, although standard food-preservation instructions don’t establish how autograph ink will behave. This is a practical experiment, with some risk to the signatures. [University of Georgia drying guide](https://nchfp.uga.edu/papers/UGA_Publications/uga_dry_fruit.pdf)
5. **Once thoroughly dry, store them in a closed container with fresh silica-gel packets**, supported so they won’t rub against anything. Check periodically for moisture or mould. Silica gel controls humidity in an enclosure; a few packets won’t reliably dry a whole fresh orange. [Canadian Conservation Institute](https://www.canada.ca/en/conservation-institute/services/conservation-preservation-publications/technical-bulletins/silica-gel-relative-humidity.html)

On your other options:

- **Refrigeration:** useful as a temporary holding measure, but the fruit will eventually deteriorate.
- **Freezing:** useful for keeping it frozen, but thawing softens fruit because ice crystals damage its cells. I’d avoid it for a keepsake intended for display. [University of Minnesota Extension](https://extension.umn.edu/food/preparing/cooking-at-home/food-preservation/freezing)
- **Varnish, hairspray or resin:** avoid applying these directly unless you’ve tested the exact ink and peel combination. They may smear the signatures or trap moisture.

Keep the finished pieces in darkness most of the time: some felt-tip inks fade rapidly in sunlight. [Canadian Conservation Institute](https://www.canada.ca/en/conservation-institute/services/agents-deterioration/light.html)

A container and silica-gel packets are the supplies I’d prioritize within your $40 budget. There’s no dependable lifespan for a signed orange peel, so the photographs are your strongest backup.