When I took this picture I used a DSLR that was definitely at the budget end price wise. It was also getting on a bit. But that just goes to show you can still get the shot with some patience.
The trick here is to get a shot where the captive otter doesn't look captive. The otters in this enclosure are quite used to human presence and are as inquisitive about us as we are about them. It meant I could get relatively close so a huge expensive lens wasn't necessary. The well designed area also looked fairly natural if you chose your spot.