First of all, it's rather frivolous to ask for a hard disk with a microcomputer in 1977. If one could afford a hard disk, one would buy it with a mini. And even then it would be rather an SMD drive.
The only hard drives (as in non-exchangeable, fixed closure) available in 1977 were the namesake Winchester drive (IBM 3340) and its direct follow up of 1975 (3350). A 3350 would cost you about 75,000 USD, offering ~630 MiB storage. So spending another 20 grand on a mini with controller might have been cheaper than building an interface to fit it to one of above micros - beside that, in 1977 even floppies where still considered optional on mini computers - and unavailable for either of the above micros.
In 1977 CDC's SMD drives were widely available, standardized and comparably cheap. A good example for 1977 would be buying the DEC RPJ04 bundle (RP04+RH11 Controller). This would offer 80 MB at 'just' 37,000 USD according to DEC's price list of 1977. Now your micro just needs to speak Unibus.
DEC is a good marker, as they tried to be the cheapo, at least until the late 70s. A RK01/03 was already available at less than 3000 USD ... but also only holding 1.6..2.5 MiB, so not really much past what a (cutting edge) floppy could offer at a similar price.
And then there was the RK05, and its compatibles. In 1977 a RK05 (alike) would be around 5-8 grand, including DEC compatible controller while offering a whopping 5 MB.
The biggest bang for the buck would be a CDC hawk drive with 10 MB for under 3,000 - plus another 2,000+ USD for a controller. Plus cartridges, of course.
Long story short, connecting a hard drive to a micro in 1977 wasn't anything even the weirdest of all geeks would dream of. Give it 2-4 more years and then we start talking.