I came across this old FM Walkman.  Seems to be Sony's first FM Walkman model from 1980.  Works perfect and looks to be in very good condition.  It is missing the belt clip though. Anyone have an idea on the value or willing to make an offer?

I have one complete with belt clip.   From my  experience the market/collectors of FM only portable units is MUCH smaller than for Walkman/ Boomboxes/ PCDP's.   My guess would be $20 to $35.  eBay probably your best chance but take more photos and best is a video loaded up on youtube put into your ebay auction proving it works well.

past 60 days ebay SOLD listings show ten sold 

Vintage Sony Walkman SRF-40W     View similar active items | Sell one like this

Time left:Nov-09 15:12

$62.80 8 bids   +$10.00 shipping

Vintage Sony SRF-40W FM Stereo Walkman with case MDR-2L1 Headphones     View similar active items | Sell one like this

Time left:Nov-11 11:19

$59.99 Buy It Now Free shipping

Vintage SONY WALKMAN LOT WM-F100 SRF-40W with Carrying Case   View similar active items | Sell one like this

Time left:Nov-21 18:49

$49.00 Buy It Now +$8.05 shipping

VINTAGE SONY SRF 40W WALKMAN STEREO PORTABLE RADIO w/LEATHER CASE,MINT CONDITION TWO HEADPHONE OUTPUT,BELT CLIP,LEFT-RIGHT SEPARATE CONT     View similar active items | Sell one like this

Time left:Nov-14 20:10

$51.00 2 bids   +$5.99 shipping

VINTAGE SONY SRF 40W WALKMAN STEREO PORTABLE RADIO w/LEATHER CASE, VG CONDITION   View similar active items | Sell one like this

Time left:Jan-08 15:02

$49.99 1 bid   +$6.99 shipping

 

VINTAGE SONY SRF 40W WALKMAN STEREO PORTABLE RADIO w/LEATHER CASE, VG CONDITION TWO HEADPHONE OUTPUT,BELT CLIP,LEFT-RIGHT SEPARATE CONT     View similar active items | Sell one like this

Time left:Dec-16 20:36

$41.00 8 bids   +$6.99 shipping

Sony fm stereo walkman srf 40w     View similar active items | Sell one like this

Time left:Dec-15 08:18

$19.00 10 bids   +$8.05 shipping

VINTAGE SONY SRF 40W WALKMAN STEREO PORTABLE RADIO w/LEATHER CASE, VG CONDITION     View similar active items | Sell one like this

Time left:Dec-13 08:50

$21.99 1 bid   +$4.99 shipping

VINTAGE SONY FM WALKMAN Model SRF - 40W / WORKS GREAT   View similar active items | Sell one like this

Time left:Dec-08 17:13

$15.00 1 bid   +$8.13 shipping

SONY FM WALKMAN Model # SRF-40W     View similar active items | Sell one like this

Time left:Dec-03 10:28

$14.99 1 bid   +$4.99 shi

Great.  That's just what I was looking for.  Appreciate the research!