Given your vague location, you're on Sprint's network (Boost is a Sprint MVNO) and Sprint has excellent coverage in Illinois, I can only recommend based on best general coverage provider in the area... which will either be a Sprint MVNO (no really terrific cheap ones exist since P'tel went to T-Mobile), or an AT&T MVNO. Given you're barely using $5 a month on Boost's 20¢ a minute Pay As You Go, I think the best recommendation anyone can make will be
Airvoice Wireless' Pay As You Go for both cost and coverage. It's 10¢ per minute and text (half of what you were paying), $1 a month maintenance fee, $10 gets you 90 days of airtime, and unused balance rolls over so long as you keep the account active. (Coincidentally, this is the cheapest to maintain prepaid service available right now period, too.) I would still check their
coverage map for your area first, though. As for phones, any old cheap AT&T or carrier unlocked handset with clean IMEI will be fine. You should be able to pick one up off CL, Ebay, or Amazon easily for under $25. (Heck, you could buy a cheap AT&T Go Phone and just stuff in the Airvoice SIM card if you wanted, you just won't be able to do MMS, WAP or web access.) The classic Nokia candybar handsets are always a good go-to, as are the ruggedized Samsungs.
If you want to stick with a Sprint MVNO, the only real alternative is going to be
EcoMobile, where your minute costs will be a quarter of what you've been paying, texts will be a tenth, you'll have roll-over, but you'll be in for $10 a month and you'll still have to purchase a new handset as you won't be able to bring over your Boost phone.
As for VoIP service, NetTalk is certainly an option, and the quality isn't near as bad as Magic Jack is, but there's also other options out there better for less depending on how involved you want to get with configuration and your average usage patterns. If you want to do the NetTalk thing anyway, contact
Ladymaier here on the forums... I know she's been using them for a few months now.
If you want to see a list of more MVNO cell phone carriers and VoIP providers, give the
superguide a look.