What is the condition of the rest of the van? Even if you were to have to spend $3K to replace your transmission, what could you buy to replace your van with $3K?
The advantages of keeping your van are: 1) you already own it (and it's presumably paid off), 2) you know its maintenance history, and 3) it's probably the least expensive option as far as transportation options go (unless a family member donates or leaves a newer, low-mileage one to you).
My sister has owned her '99 Ody since new and just paid $5K for its third tranny at about 150K miles. She will keep it until the engine dies. I have a 2001 with almost 150K miles on it now, and I plan on owning it for at least another 10 years (I just bought a "parts" 2001 van with one dead cylinder and a weak tranny for $100, so I now have spare glass, sliding door parts, engine accessories, etc). I do most of my own work so I am not worried if my tranny bites the dust (but still would really tick me off, but I really like the van otherwise).
It's really up to you. Like the above poster said, there is a lot to read on here regarding transmissions. You can search on 'gator' and 'jasper' remanufactured transmissions, as many have had success with those for a reasonable cost (going to the dealer like my sister did is the MOST EXPENSIVE option, but they did it because the van was dead over 200 miles away from home and they didn't want to deal with towing it to a less-expensive independent shop closer to home).