Amazon.com has Select Faucet Aerators and Plumbing Fittings on sale for the prices below. Shipping is free with Prime or on orders of $25 or more.
Niagara Conservation Faucet Aerators
Delta Lever Diverter Stem Extender Assembly (RP25592) $1.21
For 2600 and 2800 series tub/showers
Orbit WaterMaster Underground 3/4-Inch Brass Quick Coupler Valve (51029) $4.28
BrassCraft Delta Stop Hot/Cold Faucet Stem Assembly for Scald Guard Pressure Balance (SWD0229) $4.04
For Delta Faucet 600-1600 pressure balance faucet series
Alternatively Home Depot also has Select Faucet Aerators and Plumbing Fittings on sale for the prices below. Select in-store pickup where availablie or shipping is free with orders of $49 or more.
Niagara Conservation Faucet Aerators
1.0 GPM Tamperproof Female Thread Needle Spray Faucet Aerator 6-Pack $2.70
more
Valves
Delta Lever Diverter Stem Extender Assembly (RP25592) $1.21
2600 and 2800 series tub/showers
Orbit WaterMaster Underground 3/4-Inch Brass Quick Coupler Valve (51029) $4.28
BrassCraft Delta Stop Hot/Cold Faucet Stem Assembly for Scald Guard Pressure Balance (SWD0229) $4.04
for Delta Faucet 600-1600 pressure balance faucet series
more
TOTO Single-Control Pressure Balance Shower Valve (TSPTM) $16.38
TOTO Single-Control Pressure Balance Shower Valve w/ Diverter (TSPVR) $20.80