Nice work on your repairs! And yes running it like that is OK, I would worry about if you exhaust manifold gasket let go, that's bad news to run in the cold very hard on engines.
Look, I have done my own exhaust repairs on all my person vehicles. Even used flex pipe in the place of a resonator on a 98 mercury tracer. Worked very well for a Car I was only making it through college with and then 1 more year after that. Home done exhaust repairs save ALOT of money.
The battery cables of my f150 corroded out. Went to buy premade, well 78$ for positive and 85$ for neg..... ah wait what? This was the only premade they had. Well, I converted my pickup to marine post because 2 years of working in a truck shop taught me how to make my own battery cables. I had 4 gauge welding cable, battery lug ends and the tool to properly crimp them on! Easy with so much practice on trucks. Installed heat shrink tightly over the lugs and DONE! Costed me no money what so ever! Already had the parts. The 4 gauge welding cable was found in a trash can. I found maybe 12 feet of it with lugs that were corroded out. Cut off ends and it was new cable underneath.
Making your own repairs instead of buying premade things can save a good amount of money. Its what work taught me. You can get by just fine with out it. None the less a similar muffler for 150$ is perfectly fine as long as it is similar quality.