This is very much a question that depends on where you live.... It would really be good if you could go to the "User Control Panel" button near the upper left corner of most screens, and fill in the location info in the appropriate spot... Also answer the questions that JohnB was asking - the more info you give us, the better we can help out...
In the US, I've seen a fair number of accessible converted vans listed on Ebay, the high mileage / older models get down into the ~10K USD range...
Also depending on your friends age and disability, it may be worth talking to your states "Rehabilitation Commission" - they will often help pay for adaptive vehicles if it will help a person re-enter the workforce...
(I'm going through the process right now - my van will shortly be on it's way to Braun for conversion, I'll be back on the road in about 2 months...

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The way it works (at least in MA) the rehab people will pay for the conversion, but you have to purchase the new or very lightly used van. However there are also various low interest / long term "Assistive technology loans" that can help with that part....
ex-Gooserider