Economics of scale will only favour DIY over send off to offset if runs per issue are fairly low.
It depends on how many flyers you intend to produce over what time frame.
Larger printers cost more initially but bulk ink is cheaper , remembering that ink is a major expense.
HP printers may require specially coated HP papers. Your flyers may only require a much cheaper but nice coated stock.Dyes are cheaper than pigmented inks and should last long enough for flyers.
Thermal printers are much faster than piezo printers, and quality is now quite good , but not for fine art.-yet.
Hope this helps