I use a treeless saddle and LOVE it, but you get what you pay for... I use a Bob Marshall endurance type saddle and a Black Forest English type saddle.
Most treeless saddles require a good pad as well. I use a treeless Skito and a ThinLine pad. My whole pad set me back, used saddle and new pads, around $1,300. Other good pads for treeless saddles include equipedic, supracor, saddleright, toklat ultracell, etc. You want a good shock absorbing pad that provides some spinal clearance.
For saddles, stick with quality name brands like ansur, bob marshall, barefoot, torsion, freeform, treefree, black forest, bandos (an okay saddle), mackinder, heather moffett, sensation, etc.
Stay AWAY from hilason, sydney saddleworks, maya, freemax, or any other "no name" type brand. If it sells for a "too good to be true" price on ebay or off, just say no
If you just want a saddle to play around on, then go with a Cashel Softsaddle. You can get them new for around $275, and you shouldn't need any special saddle pad. The only horses they don't work for are those with REALLY high withers or a protruding spine.