Sorry to hear about the leak.

Unfortunately, there are probably no cheap solutions. However, if you are going to spend money to fix it, then you might consider spending a bit of extra money and making massive improvements.

What are your goals for the pond? Three feet of depth might just make a goldfish pond, but not much more than that.

Is your pond filled from surface run-off? If so, does it have an adequate watershed to keep it full?

I am asking because it would be nice to drain the pond during your driest period and then have it re-fill during the next batch of rains.

Work would be to have an excavator cut your dam and remove the existing leaking pipe. Install a new pipe with anti-seep collars and tamp it in with clay. Then you need to compact some clay-rich material in lifts to repair your cut. This needs to be done properly because it is a little bit difficult to get the repaired section to knit well with the edges of the old dam.

While you have the excavator on site, you could remove the existing muck in the pond to gain some depth. You might even be able to deepen the pond - if it naturally bottoms in a clay layer. If your "bottom" was constructed to provide a seal, then you cannot excavate through that seal to deepen the pond, unless you re-seal the pond.

P.S. There is one possible "poor boy" solution. That would be to fill your existing outlet pipe with concrete and then install a siphon system for your new outlet.

I would get a water pump and some small diameter pipe and try to wash out your outlet pipe from both ends. If successful, then pump a lot of water from the pond down the pipe for a final flush. Cut back the downstream end until you get to solid enough pipe to effectively install a plug. Then fill the pipe with concrete from the pond side. I would rent a concrete vibrator with the longest reach possible.

If the existing leak path of your pond is rust holes in the pipe with water entering the holes near the inlet, then that fix MIGHT work. If there are holes in the pipe in the middle of the dam, and water exits the pipes and leaks out through the dam material, then that method will not work.

Congrats on your new pond. Good luck on your repairs!