Now, think, would you send those items to an escrow? If not, they're not collateral. Also keep in mind than I don't know if you'd actually find an escrow that'll work with physical goods.
With physical goods you may do better at a pawn shop.
Even if someone accepts to escrow these coins, I was trying to find their value. The best price that I found on eBay is £450.00 for
1971 2p New Pence Coin and £250.00 for
Rare 1982 Twenty Pencethat's a total of £700.00, or ~$968 (1 USD = 0.72305 GBP today) which is much less collateral than the amount requested.