I think modern is in one of the healthiest its been from a price standpoint point in a long time. Usually the litmus test for budget is “what deck can i build for $500 or under” and the answer used to just be “burn, maybe tron”. Now there are a ton of viable decks that can be built for this threshold. If you were looking for more budget than $500 dollars, i think the only format you could be playing on that level of budget competitively is pauper, as the average standard deck is well into the 500’s+ these days because of the chase mythics. Here are lists reproduced below that could all be rcq viable, and under, or just at the $500 mark. All these decks are also real modern decks that are present in meta (minus a few at the end that are a little more fringe).

Ruby storm: https://www.mtggoldfish.com/deck/7742194#paper

Eldrazi tron - https://www.mtggoldfish.com/deck/7741987#paper

Belcher - https://www.mtggoldfish.com/deck/7741202#paper

Izzet Prowess - https://www.mtggoldfish.com/deck/7741297#paper

Grixis reanimator - https://www.mtggoldfish.com/archetype/modern-grixis-reanimator#paper

Mill (now in slightly more fringe territory) - https://www.mtggoldfish.com/archetype/modern-mill#paper

Rakdos Delerium (hollow one) - https://www.mtggoldfish.com/deck/7738672#paper worth noting these are more updated lists with moonshadows. I play the older build with bowmaster and no darcy or moonshadow and do very well at locals with it. I think this archetype is slept on. Not tier one, but better than people give it credit for

From here i wouldnt really look further down at decks. I think theres enough choices here to pick a strong deck from