PIC32 seems like a decent fit, you can do all of your development on free software (MPLAB and Harmony) and your programmer is $50.
Another vote for the Microchip PIC families. The free development environment works pretty well, and you can optionally buy "better" versions of the compiler on an annual or monthly subscription basis at anytime. You can also obtain a free 30 day trial period of the "better" versions to see how it works for you, and the development environment will do a real-time comparison to estimate how much code/data space you'd save with the "better" version. To be honest, I've done all of the above yet have reverted back to the free versions because they've been more than adequate for my needs.
Customer support from Microchip is remarkable. Their support tickets get real attention from staff within very reasonable amounts of time. In one case, I raised a question and was asked if it was OK for them to set up a conference call with us to discuss it in real time. They weren't kidding around, they had at least two silicon engineers, at least two app engineers, and at least one sales and one management on that call! They stayed on the phone for an hour running through things, making sure we had a meeting of the minds, and copied me on the internal emails that addressed the question going forward. Best customer service I've EVER received in the component industry. (Funny side note: During the call we reminded them we aren't their largest customer, that year perhaps consuming 10K MCU's from them. They replied that they know smaller shops are their bread and butter and the mandate to support smaller shops comes straight from the top of the company. Sounds good to me!)
The PIC's themselves have a bit of an odd MCU architecture but so far, when optimizing with hand-coded Assembly, I haven't had a reason to pound the table in frustration. Easily 95% of our firmware is in C/C++ so it's an edge case anyway. Their compilers are reasonable, have good libraries, and the head of the team that writes/maintains them personally hangs out in the Microchip forums. I'd say 50% of the threads raising questions about the compiler have an answer from that guy.
Their on-chip peripherals are quite good, and I keep being amazed at what can be done with them to push functionality onto the hardware instead of the firmware. They have an MCU selector on their website that makes it easy to dial in the models that contain the peripherals, pin counts, etc. that you need for a given project.
Finally, they have a nice range of debuggers. They sell one for $15 - not a typo - and the PICkit series is the ~$50 unit mentioned by KC0PPH above. Those are considered hobbyist level, the baseline professional unit is the ICD3 which has been recently replaced with the ICD4. Compared to the lesser debuggers the ICD series uses "production" programming voltages, has better hardware breakpoint support, etc. I've yet to hear from anyone that "needed" the ICD4 nor any better features unique to that unit, but the good side effect is Microchip is flushing out their stock of ICD3's right now for $99 each in their company store. I just picked up an extra one as a backup, at that price it's really cheap insurance. So if you go with Microchip, just spend the $100 and start with their professional-level ICD3. Since all the software is free, you're still only $100 out of pocket. This one debugger will work on almost every MCU they make, it gets transparently reconfigured with free firmware when you switch devices. By the way, Microchip shipped mine UPS Next Day Air yet shipping was under ten bucks.
There are plenty of good MCU choices out there. Just wanted to give some background on why we like Microchip. Report back on what you decide!
Disclaimer: No connection with Microchip except as a very happy customer.