Hey Matthew!
I'll second what @John Warren wrote above and add my 2 cents. Take this with a grain of salt because we do medium-end flips on the NW side of Chicago (ARVs = 600k-950k). That being said, I am still very budget conscious (raised a good Jewish girl & frugal LOL) and absolutely love the creative aspect of designing homes. I usually search for hot things on Pinterest, Houzz, and other designer's IG pages. Then pick the ones I like, put my own spin on it, and match those options to the budget friendly versions.
Some of my favorites that I believe will appeal to the majority of buyers AND not break the bank are as follows:
Kitchen- white shaker cabinets, or two-toned (as John mentioned). Sounds like it might be a smaller kitchen, so if you don't have an island or peninsula, then I'd stick to a single color for cabinets. Backsplash- you could run the quartz countertop up the back a tad, or use something simple like a 3 x 6 subway tile, maybe in a different color (if your cabinets are white), and/or a herringbone pattern. The change of pattern will really pop and only cost you some extra time.
Hardware - Black matte is still hot. Chrome is classic and IMO will never die. But black matte just gives the impression of 'luxury' to most people viewing it and costs virtually the same as chrome and brushed nickel (which I cannot stand persoally). Simple ways to elevate the hardware are to use knobs for the doors and nice modern pulls for the drawers. The little mix-match of hardware costs nothing extra and just shows you are more creative than the average rehabber.
Countertops - quartz. So many options available. Beautiful neutral options are Calacatta Laza, Calacatta Gold, or Statuario. All are white (bright or warm white) and have either subtle grey and/or greige/pale brown veining.
Plumbing Fixtures - black matte to match your hardware. Pull down, high arc faucets are still very popular. Amazon has a plethora of black matte stuff.
*Note- the nice thing about black matte is it is super easy to match. If you choose chrome or nickel (or brass/gold), matching shades and tones can get challenging. I'd stick with black matte throughout the entire place if you can swing it.
Bathroom - Furniture style vanities are nice with soft close drawers and doors. They're a little bit more than el cheapo vanities but that soft close makes a huge difference. White is always a great color OR very popular these days is a natural oak color vanity. Distressed, textured, reclaimed appearance vanities. Anything that looks natural basically, like you would find it in nature. :) (**Note: I love floating vanities in powder rooms. However for the main bathroom(s) I feel they lack the storage space I desire, so I'd use a full size vanity unless you have a lot of extra storage throughout, closets, cabinets, cubbies, shelves, etc.)
Tile: Subway tile is still in, but perhaps try using a larger option, like a 4 x 16 tile. I used this in one of our recent properties in the 'kids' bathroom and it looked a little more unique than traditional 3 x 6. I also recommend hexagon flooring. I used a semi-polished white hex floor (8 x 8 or 11 x 13) in the master, and a green matte hex floor in the kids bathroom for a pop of color. Hexagon flooring is still very popular and affordable. (*If you're looking to go a little bolder, something like the Adessi Kavala Matte White Hex tile is a super cool option for a bathroom floor or accent wall in the shower or tub area.
Floors: Do you have wood floors? If so, sand and refinish. Stain them a nice, light, neutral color. And if possible, keep the finish matte, not shiny. Dark, shiny floors are old hat these days. People want light and bright and inviting. If no wood, then an LVT is a nice affordable option (I'm sure you know since you have other rentals). Floor & Decor has incredible options at all price levels. Again, go lighter.
Paint: Grey is nice but I'm leaning more towards Earth tones. I've seen a lot of pale, pale browns, neutrals, light beiges, light taupes and pewters, etc. And of course, white. You can never go wrong with white because it's a blank slate. We recently did the following in our house: Benjamin Moore 'Dove White' on the walls (satin or eggshell finish), trim (semi gloss finish), doors (semi gloss finish), and ceiling (flat finish). Yes, we used the SAME white for the entire interior of the house and it looks INCREDIBLE. And guess what? It MATCHES perfectly because it's the same color with different finishes! :D We used BM 'Simply White' and 'Pale Oak' on the exterior of the house.
Light fixtures: Don't know the style you're going for, but modern original, boho modern, farmhouse, industrial farmhouse, mid-century modern, and modern farmhouse are all very popular styles that will appeal to a large buying pool.
If you want to see some of what I've referenced above, feel free to look up our property online. If you DM me I will give you the address. We just went live yesterday and there are more than 50 pictures available. If you'd like any referrals for vendors or suppliers for good pricing, let me know. I shop a lot online :)
Hope this helps!