Can my spouse and I use the same lawyer?
No, in nearly every case one attorney cannot represent both spouses in a divorce. Once a case is filed you are opposing parties in the same litigation, and that is one of the few conflicts a client is not permitted to consent to. A small number of states allow a narrow exception for a fully agreed, uncontested case with informed written consent, California and the District of Columbia among them, usually only where everything was settled beforehand and there are no children. It is the exception, it is disfavored, and being amicable does not by itself qualify you for it.
The reason is structural rather than a judgment about your relationship. A lawyer owes each client undivided loyalty and confidentiality, and in a divorce the two of you are dividing one finite pile of money and time with your children. Every dollar or overnight that goes one way does not go the other. That makes your interests adverse in the legal sense even when you are being generous with each other, and no lawyer can advocate fully for two people on opposite sides of the same line.
What you probably actually want
Most people asking this are not asking about ethics rules. They are asking why something they both agree on has to cost twice as much. Three arrangements are real, and one of them likely fits.
One lawyer drafts, and the other spouse has it reviewed. The attorney represents one of you, prepares the agreement and the filings, and cannot give the other spouse legal advice beyond telling them to get their own lawyer. Do not wait to be told that, either: the duty to correct the record only bites once the lawyer knows, or should know, that you have the wrong idea about whose side they are on. Assume the drafting attorney is your spouse's. The unrepresented spouse then pays for one consultation to have it reviewed before signing. This is common, it is far cheaper than two retainers, and it is usually what people mean when they say they want to share a lawyer.
A mediator works with both of you. A mediator is a neutral. They help you reach an agreement and can write it up, but they do not represent either of you and cannot give either of you legal advice, even when the mediator is also an attorney. Being an attorney-mediator does not make them your attorney. A mediator should also talk to each of you privately about safety and pressure before you start, and keep watching for it as they go. That is a professional standard, so if it never happened, say so.
A limited-scope arrangement. Some attorneys will handle one defined piece of work, such as drafting a settlement agreement or reviewing one another lawyer prepared, rather than taking the whole case. You pay for the piece, not the representation.
The part worth being careful about
The cheap paths all assume the two of you are roughly evenly matched: both of you can see the finances, both of you can say no, and neither of you is agreeing out of fear or exhaustion.
Where that is not true, the arrangement stops being efficient and starts being one-sided. An agreement drafted by your spouse's attorney is written to protect your spouse. That is the job you are paying them to do, and it is not a criticism of them. It is the reason the review consultation exists, and it is why skipping it is the expensive kind of saving. There is more on that imbalance in what happens when your spouse has a lawyer and you don't.
What this means for cost
If you genuinely agree, your realistic floor is not two full retainers. It is a mediator or one drafting attorney, plus one review consultation each, plus filing fees. The four ways to get divorced covers what each path runs and, more usefully, what actually drives the bill, which is how much the two of you disagree rather than which professional you hire.
Mediator credentials are one of the least standardized things in this process: some states license and regulate family mediators, others do not, and "certified" can mean very different things. Ask what training a mediator has and whether they are also a practicing family-law attorney before you hire one.