That's a heavy boat and will be tricky to launch without a trailer with a 25 on the back or even a 15, you'll be OK on a slipway with transom wheels though but not on a beach really.
Not the quickest thing to assemble/disassemble either if going that route each trip.
But on the upside a lovely solid old thing compared to most other SIB's.
Really needs a trailer though...
Price is OKish but depends on the engine value, worth checking ebay for completed sales to gauge market value although location always affects this a lot:
This was another 340:
AVON SUPERSPORT S3-40 COMPLETE OUTFIT WITH ENGINE AND TRAILER | eBay
Avon Supersport S3.4 Inflateable dinghy boat | eBay
Past sales to sift through:
avon in Sailing Dingy Boats | eBay
avon in Boats and Watercraft | eBay