I can't give you a current value on your Tingle rifle but IIRC they sold new for considerably more than the Thompson-Center Hawken. Since there were many fewer made, and since yours is a left handed piece, I would guess that its rarity increases the value significantly.
As a note of interest, I met Bob Tingle through a 2nd Cousin that knew him well, and toured his fledgling manufacturing operation shortly after he began production of his line of rifles. Regretably, he passed away at a relatively young age before his high quality products had a chance to impact the market. He was a pioneer in the rebirth of Black Powder shooting and produced many custom Black Powder arms before his venture in commercial manufacturing.
I'd love to see pictures of your rifle giving me a trip down memory lane.