We had a 17.58-1 with 4 kids, if your happy to loose the dinette then do so. Maybe look at one of those gas lift table legs I am thinking to get one for the 22' as with the 17' I just left the table at home and left it a bed always.
I really liked the Basestation although we where not sold on the expanda bed.Hire a Expanda see if your happy with the bed.
Its not a cheap purchase we changed over within 18 months so lost $'s at the time we thought we only have space for a 17' and Sarah did not want a toilet. Twins Asthma and cold weather changed the Toilet situation and I made room for the bigger van.
If your wanting to keep the Prado you have to go touring on the 17' a touring 18' might fit as well. Not sure a OB will come under 2500.
There are a few other brands around that can do a van under 2500 ATM for the Prado with triple bunks.
Depends if you want to buy new or secondhand.
If you want triple bunks a few around like Kokoda.. ..
http://kokodacaravans.com.au/product/battalion/
second hand New Age Mantra Ray etc that could come in under 2500.
Coromal have a E636S 20' that could be under.
JB Caravans
Kingdom
Not sure a 20" Starcraft touring with triple bunks ends up? our 22' is 2780 so over the 20' I assume will be less?
its never ending if you like the 17' just work out if your happy to drop the dinette down.
We are there now with our 22' 3 bunks and 4 kids. Twins head to toe at the moment
We either move one to dinette again or kick the eldest into the annex