www.findartinfo.com/  will give you prices up to the end of 2015 with limited information at no cost.... 

I use Artprice and I find it usefull.

It's cheaper.

I use Artnet, Artprice and Gordon's. Artnet is painfully expensive but frankly has no equal when it comes to researching paintings, works on paper, etc, I don't even want to say what it costs me per year.

Out of interest what are you going to be looking up? In this I mean will it mostly be prints ? If so I'd suggest you try Gordon's.

Gordon's is the professional print price database, it's a one off fee for annual online access (IFRC about $500 p/a with the photography database as well) It's absolutely incredible and the information in gives far exceeds any other database for prints, even Artnet. However, you need to know how to use it, there are no images, and you'll need to know the name of the print or the catalogue raisonne reference in order to look something up, but it has prices that go back to the mid 80s. It will give you global price results in multiple currencies on exchange when sold, and often give you fuller cataloguing detail than Artnet provides. It's not the easiest to navigate but it's brilliant.

www.gordonsart.com

Oh and one order gives you 2 user names so you can share with a friend if you want to.

As expensive as Artnet is, it's by far the best! I have no experience with this but i know some people who use Auction Club as an alternative.

Barnebys has a free realized price database that is very helpful.

www.barnebys.com/auctions/?o=0&qsp=a&a%5B%5D=198&q=&a%5B%5D=198&a%5B%5D=198 is a link to the Julien's catalog

www.barnebys.com/realizedprices/banksy.html?minprice=0&maxprice=189000000&o=0&tc=0&r1%5B%5D=0&a%5B%5D=0 is a list of realized prices of Banksy works that have sold

Sorry, the hyper links weren't working so I just included the full links.

For some reason the hyper links didn't work so I just added them.

I use Artnet as well and it is expensive at 10 searches per month plus additional fees if you go over. That being said, one search encompasses the last 100 auction results for the artist... If you search an additional 100 results (last 200) that counts as 2 searches out of 10 for the month. Just something to be aware of.

Either free or with subscription?

Not that many regrets, except for not buying a Banksy Flags for £4k two years ago because I thought I'd have a think about it and then maybe buy in a couple of months (by which time it was nearer £20k).

Oh and a massive Sebas Velasco original that I forgot to bid on and sold for about £700. I'm still annoyed about that. 

Got a lot of old emails about watched Banksy items that I thought were too expensive to commit to.

Sold many a print when I was a poor student for 2k. Kicking myself for selling a Nola Grey for 3k. Probably worth 150k now.

I once sold a Stop and Search print to someone (for 2.5k) who, on arrival claimed it was creased. I had videod myself rolling it and packaging it so it clearly wasn't me. Never found put what had happened tbh. After I sent them the video he didn't get back to me. I suspect his wife opened it and rolled it up side to side against the grain.

A well trodden conversation.. who what when... etc.

i remember seeing around 10 banksy prints flying by one evening on ebay - a collection sold.(same id)
circa perhaps end of 07 (certainly someone thought clearly at the time.. yeah time to get out take the money now).

not sure if that person still has the same view.

..and yeah i was pipped at the post on several of said prints.

hey ho...