Your advised strategy shows me you are not from this parts of the hood.., where mostly clothes are already mtumba so a 2nd hand mtumba from a hard working individual won't be in a good condition to be swapped let alone given for free...
Anyway my advise on saving is first to take stock of your life...., account everything you buy and consume for a month, a can of soda, bottle of water, mkaa kwa mama watoto, nyanya mchele matumizi ya ndani, lunch, even drinks in the evening, mafuta kwenye gari n.k.
After doing that you will know what everything costs and what cost more and were you can save hence maybe instead of buying rejareja matumizi ya ndani you can buy in bulk, instead of eating out every afternoon you can carry a lunch box, and instead of passing to the bar every evening you can buy a crate and drink at home, or maybe you can decide to save some of your energy kwa kumfungulia mrs banda la nyanya kama hafanyi kazi ili achangia matumizi ya home