My response is going to vary depending on provider and budget. Since most CDMA carriers outside of Ting and PagePlus don't really do BYOD, I'll stick with GSM recommendations.
The great advantage to smartphones is the flexibility in what you can do with them given the software selection that you can install on the things, and their ability to competently access the internet. As such, they're great
tools for keeping communications costs low and having the flexibility to be the digital equivalent of a Leatherman multitool, but they also can prove to be too much of a temptation for some folks and quickly morph into more of a distraction than a tool. If you've been reading the forms for a while, you've likely already seen how some of our fellow mustachians still have trouble short circuiting their adaptation to the omnipresent internet in order to kick the mobile data habit. If you think this might happen with you, consider alternatives. Anyway... recommendations!
A good older model Android phone to consider would be the
LG Optimus One refurbished off Amazon or something... should go for between $75-125. Left stock, the phone's a pretty solid basic smartphone (even if it's old) but won't win any high performance ratings, but with some hacking and tweaking takes well to
CyanogenMod if you're into that sort of thing. Probably suit your needs relatively well.
Next up the GSM smartphone chain would be the
HTC Nexus One for between $130-190 refurbished and unlocked. This is the first of the official flagship Google phones, and is also well supported by CyanogenMod even if Google
EOL'd the upgrade path at 2.3.6 (Gingerbread).
Final on the Android list would be the
Samsung Nexus S, which is still receiving official OS upgrades from Google and runs used/refurbed in really good condition between $150-250.
If you're into the whole Apple scene, the
iPhone 3GS is still receiving iOS updates (though will likely hit EOL with Apple soon enough), and an unlocked and refurbed unit can be had for around $140-240 depending.
In general, you can't go wrong with any of the Android smartphones that are official
Google Nexus phones or can
"officially" support CyanogenMod, but checking out online reviews of the hardware is always beneficial, as things like the speaker, microphone, screen and reception are more hardware limitations than software. I won't bother recommending much more expensive as that starts hitting anti-mustachian territory for most folks, and given you've been living on a feature phone all this time, probably wouldn't benefit you any.
Of course, the prices are just estimates of average going on Amazon and Ebay for quality refurbs. You may or may not be able to get cheaper off CL or elsewhere through private party, but then you have the issue of a possible hot device on the IMEI blacklist or an abused phone or an assortment of other unknowns. Personally, I'd be comfortable going that route, but I also know what to look for. YMMV. If time == money, sometimes it's just easier spending the extra if you're sold on a specific make and model to get the refurb from a reputable reseller.
If you'd rather keep going with a dumbphone and iPod Touch or $30 MP3 player that takes SD cards and a $90 offline GPS or, or, or... that's not a terrible idea either. Frequently, and especially on the lower end, all-in-one devices are mediocre
at best at nearly all their tasks. If you want to do a basic dumbphone, the
Samsung B2100 is a ruggedized and nigh indestructible candybar form factor feature phone that you can pick up unlocked for under $80 brand new. Extra bonus? It's got decent MP3 playback functionality and supports Micro SD cards up to 8GB.
Hope that gets you started.