buy new, i'd go for a trafic 2900 with air con, 1250kg payload is enough
This is exactly what I've got!
Sport.
Box fresh.
They can be had for £14k if you argue the toss.
When i go to renault site, they start from like 22K where am i going wrong 
That's list price.
Ring a dealer.
Autotrader-click new vans.
The absolute best way to get your best price is take the time to find every Renault dealer in the country. There aren't actually that many. There may be 20 'Smiths Renault' spread across an area.
I mean different named dealers.
You tell them exactly what you want. A list of non-negotiables and a list of 'likes'
Tell the dealer you want a price by x o clock on x date.
You want their best price.
ALL OF THEM will say, "we can match any price". If they can match a price then they should offer that initially.
Be clear and firm, you will take their one price, no haggling, no negotiating a 'service deal' and all the other BS they try.
You will get a list of about 20 dealers I'd think.
All offering (to all intents and purposes) exactly the same van.
Go with your best price.
If you want to make it more fun.
Try Nissan & Vauxhall.
Vauxhall are the cheapest.
Renault midrange.
Nissan most expensive.
They're all made by Nissan with only minor ancillary parts by the others.
That changes next year though I believe.