Depends on what you want to do ?
If you want to get the most for it, then to be fair, you'll probably (not always) get the best price on EBAY and using the "completed listings" tab will give you the best idea of what they are actually selling for. Ignore the over-priced bikes on a "buy it now" from dealers, they circle round and round until some fool pays up... bear in mind that things do fluctuate and where the bike is will affect the price.
If you want the bike to go to an Ariel enthusiast, then stick it in the mag (cheval) which is FREE. I am not sure where the bike is, but there are lots of ariel-ists over in the europe and the mag will reach them all.
If you truly wanted to help the club and keep bikes on the road, then pass it onto the Single Spares chap, for slighly less ..
If you asked me, then I'd reckon a 350 swingarm (which I think a 1954 is) , in pieces, is maybe worth around £1500. Give or take. More if it's all there, refurb'ed and just required rebuild. (If it's a rigid or plunger, then it will be more again).
I bought a complete VH500 engine ( I assume yours is a VH) for £350 last year. If your 500cc engine goes with the bike, then it should knock the estimate up at least that much, if not more.
Photo's speak volumes and if bits have been sorted then make that clear, especially things like mags.
Correct tinware is expensive to buy now; so if that is all there then that is also a plus.
Make sure whoever buys it; JOINS THE CLUB
John "Josh" Nashwebmaster@arielownersmcc.co.uk
2009 royal Enfield,1978 t140 bonneville, '67 CJ750, 196-ish Ural M62 outfit, 1960 k750, ''51 kH500, ''49 soon to be Ariel bobber, 47 VH twinport, '44 Ariel WNG, '43 Ariel WNG, '41 Ariel WNG and piles of rusty scrap ....