While an electric miter saw is a convenience, it is not necessary to do good work. A quality electric miter saw will run around $150-$200, that by itself would destroy our budget. A hand saw with a miter box does the job just as well at a fraction of the price. This highly rated Stanley version for ~$60 should get the job done, albeit with a bit more elbow grease.
The refrigeration setup in your van is an area where you really do get what you pay for, whether you’re paying in money or in time. The best options are the most expensive. The cheapest options are a pain and/or don’t work very well. And if you try to save money with a DIY refrigerator setup, you could end up spending a lot of time on installation.