Being involved in electronics as a hobby, one possibility that presents itself is the use of a single-board computer such as the Raspberry Pi. The cost for a full system does add up a bit, but a full solution for around $50 might be possible. For instance:
Pi Zero based:
- Raspberry Pi Zero W: $10
- Enclosure: $5
- Power supply: $5
- SD card: $10
- Mini HDMI-to-HDMI cable or adapter: $5
- Bluetooth presentation remote: Around $15 (or you could use a smartphone for this...)
Pi 3 based:
- Raspberry Pi 3: $35
- Enclosure: $5
- Power supply: $5
- SD card: $10
- Presentation remote: Around $10-$15 (or you could use a smartphone for this...)
One of the benefits of this kind of approach is that the whole presentation set-up becomes very portable. My laptop is old and heavy and there's a lot of times at the con when I'd rather not be lugging it around. With a SBC-type solution like the Pi the whole system can fit in a small bag or pocket.
The Pi Zero is a very inexpensive model but there are some trade-offs in terms of convenience that can wind up pushing the total price of the system back up again. For instance, the Pi Zero has a mini HDMI connector rather than a full-size one, which means you'll probably need to provide the adapter to full-size HDMI yourself. Also, while the Pi Zero does have a USB port for connecting devices, it's a USB micro connector, so in order to use something like a presentation remote with a USB dongle, you'll need a USB-OTG adaptor. (I side-stepped the issue above by specifying the "W" version of Pi Zero, which includes Bluetooth, and using a Bluetooth remote) And finally, if you wound up needing to use composite video or analog audio rather than HDMI, that's more complicated on the Zero than on the full-size Pi models. A full-size Pi costs more and is larger but the convenience is often worth it - plus you get a more powerful (or "less weak"?) computer to work with.
There are some disadvantages to going this route as well, of course: First and foremost, there's a learning curve to deal with, if you're not already familiar with the Pi and Linux (which is the most common OS choice on Pi). And since it's not PC hardware, you might be rather limited in what software you can run on it. (There is a way to run Windows 10 on the Pi, but it won't quite be the same as running it on a full PC) It's also not a particularly powerful platform - it's low-end or mid-range smart phone hardware basically. If you run Linux on the Pi, that probably means using Libreoffice to run the presentation - and while it's a generally quite capable package that does support importing presentations from Powerpoint and other packages - importing presentations doesn't always go smoothly because of differences in the software.
One final disadvantage to note: A laptop would have its own display, and then probably the projector would act either as a second display or mirror the first one - either way, you have your own display to refer to as you're presenting. A Pi would not provide this by default. Using a smartphone as a presentation remote could get around that during the presentation.
Despite these challenges and limitations, I think it's something to consider. Relatively portable, reasonably inexpensive (though you can probably find used or low-end laptops, HDMI-capable tablets, etc. that would be price-competitive), and powerful enough for typical presentation needs - but with some limitations and learning curve to deal with.