We have a new shape Dispatch Combi and it is ace (Scudo and Peugeot Expert are also identical)- but a bit scarce 2nd hand and doubt if you will find one for your money. Also comes registered as a car so no speed limit / insurance hassles. I've made my own tubular steel / mesh bulkhead to keep kids and bikes apart.
Very late (early 2007 ish?) old shape Scudo / Dispatch / Expert Combi should be in your budget and is still a good beast.
I would REALLY go for an original factory fit version (Combis, VW window van, Merc Travelliner, Vivaro minibus or crew van etc). Treat conversions with caution and ask questions about seat spec (should be M1), testing, under floor reinforcement etc. A few bolts with big washers are not good enough in most cases…..
Trafic / Viavro crew van is a good ready made bulkhead and seat option. You can get retro fit of the same (very strong and safe conversion) for many vans but it is in the region of £2000 http://www.doublecabin.co.uk/index.htm