I use an Apera PH60. Before that I was using pH test kit drops, which are quite inexpensive and still probably a lot better than the cheap pH meters. I got the 1 oz sampler with a pH up/down bundle, and then a refill for like $10 that would last years.
I use this one. It has a replaceable probe, 1–3 point calibration, and automatic temperature compensation. You can also get other types of probes if you get into cheese-making or something. I'd also recommend buying bigger bottles of calibration solutions and storage solution.
Also be aware that the probes on pH meters need to be replaced periodically. As much as you hate strips, meters are an ongoing expense.
A bit of sage advice...from someone who 4 stepped his way to a good set up. If you're gonna do this, do it right from the beginning. Do not half step anything. You will save yourself money in the long run. Spend now, save later. I have a closet full of half step lights and gear. I wish someone would have told me what I'm telling you when started.
For 4 Plants I would suggest a 4x4 (minimum) Gorilla Grow tent:
https://www.amazon.com/Gorilla-Grow-Tent-4-4-Feet/dp/B00KCSSBWY/ref=sr_1_5?dchild=1&keywords=Gorilla+Grow+tent+4x4&qid=1621371803&sr=8-5
To light that space you'll need max of 1040 PPFD ( µmol ). So I think you have some options in the latest Quantum Board LED's. Do NOT get any type of blurple light bullshit. DO NOT. Good light options: HLG, MarsHydro , SpiderFarmer etc.
Fantastic Light for a 4x4 with room to grow into a 5x5. HLG 600 Rspec is great for the full cycle of grow.
PH Pen. MUST HAVE. Do NOT skimp on this. This is pricey but it's awesome and you can replace the head. https://www.amazon.com/Apera-Instruments-AI311-Replaceable-2-00-16-00/dp/B01ENFOIQE/ref=sr_1_1_sspa?crid=3AKN7HNLXNE1V&dchild=1&keywords=apera+ph+meter&qid=1621372495&sprefix=Apera+PH%2Caps%2C173&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyTklLNlRGQzNOS0NOJmVuY3J5cHRlZElkPUEwNjk0MDM4M0JKV0lBRksxNEQ0OCZlbmNyeXB0ZWRBZElkPUEwMDI1NjQ1MTNQOUhROUZES1JFVCZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=
PPM Meter (Yes, you need it) :https://www.amazon.com/Lxuemlu-Professional-Temperature-0-9999ppm-Aquariums/dp/B079DN9DRS/ref=sr_1_4?crid=1O00B34SNEOME&dchild=1&keywords=ppm+meter&qid=1621372562&sprefix=PPM+Meter%2Caps%2C166&sr=8-4
You'll need Fans, humidifiers, dehumidifiers, space heaters and air conditioning.
Get good soil and cut it with 30% Perlite for aeration.
Use cloth bags, or preferably, rain science bags: https://rainsciencegrowbags.com
Nutrients. Organic? Bottled? Dry Amend? SOOOOOOOO many ways to feed. I like MegaCrop by greenleaf nutrients
It's a lot. I know. I'm here to help and answer your questions. DM if easier.
I have these two.
Allprettyall Digital PH Meter PH Tester
Lol WTF all pretty all?
Apera Instruments AI311 Premium Series PH60
The allprettyall works fine after 2 years of not caring for it properly. I leave it out, uncovered, don't clean it..just treat it like crap and it's always within .02.
It's a gamble and if you don't have a second and third method of checking, then probably don't get it.
The apera one I got has replaceable probes. 3 different types of probes, for liquid, semisolid, and something else.. I Forget.
I have 2 tips for liquid, one for garden, one for pool maintenance.