There is great budget gear out there these days. The Vintage Icon series are superb basses and there are cheaper derivatives of big brands such as Markbass' Blackline series, Eden Nemesis, etc. for amps. Also names that have fallen out of fashion such as SWR and Trace can be bought fairly cheaply on here and eBay.
I used a Carlsboro Cobra 90 combo for years and a Squier Precision. That amp was lent out to many players in my locality and even became our rehearsal studio's in house bass amp - as a result I got free rehearsals! OK it was a revelation when I first played through a Trace Elliot however it did the job and I dare say it's still out there. I held on to my Precision and it sounds and plays as good as ever. I do a lot of buying and selling because I like a bargain but my two keepers are my Squier and my Gibson Grabber and though prices are rising these were essentially budget versions of top brands when first sold.
I do think the best investment is a good amp. I can make a reasonable attempt at playing most basses and I've gigged with bashed in Kay's, Hondos, and also some very posh instruments that I've regretted buying because of their complex circuitry or shininess having a good amp ( and I include my old workhorse Cobra in this as it was 100% reliable ) can make all the difference.