Since money is a consideration, I have a few suggestions too.

The Sony will also accept all A mount konica/minolta lenses, which have been manufactured since the 80's. Like the pentax, good glass can be had cheaply.

A set of extension tubes (kenko makes AF tubes) will make a standard telephoto into a macro lens, and a 1.4x tele-converter will make a 300mm telephoto into a much longer lens...all for MUCH less than the three lenses that they replace. Granted there will be some loss in optical quality and light, but it's everything on a shoestring budget...the REALLY nice lenses can come later, after you have something to start with. That way, you can avoid the frustration of not having the versatility that you want.
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Erik Williams

fattailed geckos, western hognoses, and a bunch of postage stamps.
Contact me
www.chicagoherp.org
Chicago Herpetological Society