Short answer
A good plumber's website is a one off build cost, not a monthly subscription. Monthly website deals usually mean you never own it. Before paying for a new one, check whether your existing site is genuinely holding you back or whether the real problem is an unfinished Google Business Profile.
This question usually arrives with a quote attached and a nagging feeling that the number is either too high or suspiciously low. Both are worth being suspicious of.
The two ways websites get sold
One off build. You pay once, you own the site, and it stays yours. If you fall out with whoever built it you take the files and go elsewhere.
Monthly subscription. A lower number that never stops. It looks affordable, and for some businesses it genuinely is the right call, but read what happens if you cancel. Often the site simply disappears, along with any rankings it had earned, and you have nothing to show for three years of payments.
For most plumbing businesses a one off build you own outright works out better, because a decent site should last several years with only small changes.
What you should expect to pay
It depends on how many pages you need and how much of it is bespoke. A plumber with one service page and a contact form sits at the bottom of the range. A plumber wanting pages for eight services and six suburbs sits higher, because that is genuinely more work.
What should worry you at the very bottom of the market is a site that is one page, built on a template, shared with forty other trades, and impossible to extend later. It will be cheap and it will cost you more to replace than it saved.
At the top end, be equally wary of paying agency prices for a brochure site with a stock photo of a smiling man holding a wrench.
Do you actually need one?
This is the question worth asking before the budget question.
If your current site loads fast on a phone on mobile data, says what you do and where you do it, and has a phone number people can tap, it is good enough to be going on with. Plenty of plumbers replace a perfectly serviceable website while their Google Business Profile sits half finished, which is exactly backwards. The profile is free and does more for emergency work.
If your site is slow, ten years old, or does not work properly on a phone, it will hold everything else back and it is worth fixing.
The trap to avoid
Paying a marketing retainer that quietly goes into building a website for six months.
These are different jobs. A build is one off work with an end date. Marketing is ongoing and only makes sense if it is measured. Blending them means you cannot tell what you are paying for, and it is one of the more common ways trades get taken for a ride.
That is why builds and marketing are priced separately here, with the builds living on a separate site entirely. You should be able to see exactly what each one buys, and all the marketing prices are on one page.
The thing a new website will not do
Bring you visitors.
A website is where people land. Something still has to get them there, and that something is the profile, the reviews, the SEO and the ads. A better site improves how many of those visitors turn into phone calls, which is worth real money, but it does not create the visitors in the first place.
If somebody is selling you a website on the promise that the phone will start ringing because of it, ask them what is going to bring the traffic.