Craig,
The Parker 10 gauge guns regardless of gauge are rising in value. The 2 & 7/8" "Short Ten" is a very effective cartridge which is becoming more popular within the Classic SxS realm. I think we have 10 active Short Ten shooters on this forum. The guns in shooting condition on the market, be they Parker, LC Smith, or Lefever, and others to include English guns, are not staying on the market long.
To add to what my 10 bore colleague Mr. Books stated, $800 minimum for a good shooter (mechanically solid gun, tight action, that needs NO repair) in 20% condition is not too much if you like the gun. If you find one cheaper let me know
A 50% condition 10 gauge Parker would be much more!
For what it's worth,
Mark
PS: Please consider spending $40 to join the PGCA. The collective advice provided in this thread will save you much more than that!