Motorsport art valuation

[McAndy]

Morning. I have a couple of pieces of signed motorsport art that I am considering selling. They're not worth thousands (as far as I know!) but I would like to obtain a proper estimate of their value, rather than going off the single example I found on eBay.

I know nothing about art brokering. I'm aware of Alex Reade motorsport and I was considering dropping them a line. There's also a high street chain that sells signed memorabilia, but at least one of the items may be a little too specialist for them (60s sportscar racing).

Can anybody recommend a good valuation service please? Thanks!