[J]

I am looking to purchase a “purse size” concentrator for outside mobility.  They seem to range from $300 – $3000+.   Any suggestions for budget friendly units for < 1000 and reputable places to purchase?  Would need pulse, up to 5-6L, batteries that can be switched out with about 3hrs of run time each, & lightweight under 6lbs.  Already have an ac concentrator at home, but insurance will only provide one.  Refurbished could be an option.  Thanks!