No mods? There are a plenty that I noted while doing research in the past.
RS grille - $240
ECS Strut tower brace
https://www.ecstuning.com/News/Audi_A45_S45_Front_Strut_Tower_Brace_8049/?trk_msg=FTIO1SIT5VI4NFN919JH1SKAU8&trk_contact=NRPFODNCHPJ75OTHBAHO5HADT4&trk_sid=UFPFSHCLVU7OS4AMC3TBQVK768&utm_source=emailcampaign&utm_medium=email&utm_term=ECS+Carbon+Fiber+Strut+Tower+Brace&utm_campaign=Audi_A45_S45_Front_Strut_Tower_Brace_ 09192017_EP_8049
Bilstein B12 Suspension kit - trim bump stops 1-1.5” back, cut fronts in half (or remove as it’s built-in in kit). You gotta trim the rear bump stops to avoid bounciness. And don't use the front stops cause the B8's have internal ones. 034 Motorsports upper strut mounts
https://www.ajusa.com/bilstein-b12-pro-kit-suspension-kit-46-183330
https://www.ecstuning.com/b-bilstein-parts/b12-suspension-cup-kit/46-183330~bil/
Autotech Fuel Pump - $400
http://www.autotech.com/mm5/merchant.mvc?Screen=PROD&Product_Code=10-127-101K
Alu Kreuz - $420
https://www.ecodetuning.com/eurocode-alu-kreuz-billet-aluminum-drivetrain-stabilizer-2013-and-up-b8-5-a4-a5-s4-s5-q5-rs5.html
Front upper CR-15 strut brace $150
Headers
https://www.aliexpress.com/item/Mertop-Race-AUDI-S4-S5-A7-A8-B8-Q5-SQ5-3-0-TFSI-V6-Long-Tube/32740567255.html?shortkey=uimieAfY&addresstype=600
H&R sway bars + end links
https://tagmotorsports.com/h-and-r-swaybars - $521 + shipping $10
https://www.uspmotorsports.com/Audi--S4--B8.5--2013--3.0T/Steering-and-Suspension/Strut-and-Sway-Bars/HR-Sway-Bar-Front-30mm-Audi-A4-S4.html
http://www.moog-suspension-parts.com/moog-k750359
http://www.moog-suspension-parts.com/moog-k750361
Mounts / Inserts - skip for now
https://store.034motorsport.com/034motorsport-drivetrain-mount-insert-package-b8-audi-a4-s4-rs4-a5-s5-rs5-q5-sq5-billet-aluminum.html
https://store.034motorsport.com/motor-mount-street-density-line-b8-audi-a4-s4-a5-s5-q5-sq5.html
https://store.034motorsport.com/billet-aluminum-rear-subframe-mount-insert-kit-b8-b8-5-audi-s4-rs4-s5-rs5-q5-sq5.html
https://store.034motorsport.com/apikol-rear-differential-mount-insert-kit-b8-audi-a4-s4-rs4-a5-s5-rs5-q5-sq5-polyurethane.html
Injen SP Intake - $250 (a bit of whining), 19 hp, 15 ft/lbs
AWE tuning touring exhaust w/102mm tips + resonated DPs - $2,300
https://www.uspmotorsports.com/Audi--S4--B8.5--2013--3.0T/Exhaust/Exhaust-System/Package-AWE-Tuning-Audi-S4-3.0T-Touring-Edition-Exhaust-and-Resonated-Downpipe-System-Chrome-Silver-Quad-Tips-102mm.html
http://www.modbargains.com/awe-tuning-cat-back-exhaust-audi-b8-s4-2.htm
EPL Stage 1 $1000 (possibly $699)
EPL Stage 2 + SC pulley + belt $1650 (possibly $1150) (183mm preferred over 187mm)
+ cable (Self flash) - $150
EPL TCU tune $499
https://www.facebook.com/EPLabs/
[email protected]
AWS Alpha cooling kit - the best and most expensive
https://www.amsperformance.com/cart/alpha-audi-b8-5-s4-s5-supercharger-cooler-system.html/
Motul coolant
Tires: 245/40ZR18 94Y 8Jx18 ET47 5x112 2.3
https://www.tirerack.com/tires/tires.jsp?tireMake=Michelin&tireModel=Pilot+Sport+A%2FS+3%2B+%28W-+or+Y-Speed+Rated%29&partnum=44YR8PSAS3PLXL&vehicleSearch=true&fromCompare1=yes&autoMake=Audi&autoYear=2014&autoModel=S4%20Sedan&autoModClar=Premium%20Plus
Wheels: 18”x8 rotary forged, flow forged, light
https://www.tirerack.com/wheels/WheelCloseUpServlet?target=runWheelSearch&initialPartNumber=W0171220253B&wheelMake=O.Z.&wheelModel=Ultraleggera&wheelFinish=Black%20Painted&showRear=no&autoMake=Audi&autoModel=S4+Sedan&autoYear=2014&autoModClar=Premium+Plus
StopTech 355mm BBK - $2500
Carbotech Pads xp20/xp24 or ENDLESS pads
Castrol SRF fluid or Motul rbf660
http://www.ross-tech.com/vcds/tour/acceleration.php
or
https://www.ecstuning.com/b-ecs-parts/front-big-brake-kit-stage-3-2-piece-rotors-365x38/003754ecskt2/ + https://www.ecstuning.com/b-ecs-parts/rear-brake-kit-stage-1-2-piece-cross-drilled-slotted-rotors-330x22/8k0698301mkt5/
or
https://www.ecstuning.com/b-ecs-parts/front-big-brake-kit-stage-3-2-piece-rotors-365x34/8t0615107ckt/
Rear diffuser (carbon)
https://www.ecstuning.com/b-ecs-parts/carbon-fiber-rear-diffuser/018359ecs01a/?gclid=Cj0KCQiAyszSBRDJARIsAHAqQ4rPNXISjvyyTUKaKtx D3zohXPHkJif-j2Y5WJ5LFAGJcXpX6o2VimAaAjUDEALw_wcB
Then you can add cf front lip, door projectors https://www.amazon.com/Flyox-Lighting-Shadow-Projector-Welcome/dp/B01LWP7JIP/ref=sr_1_4?s=automotive&ie=UTF8&qid=1515443605&sr=1-4&keywords=audi+door+lights etc :))
Hope that helps lol