I don't think there's any "magic" here, but here are some suggestions.
First, I assume you can't buy fractional shares. Given that, I see 4 possibilities offhand:
- Is there some other asset that's basically the same as X but the per share cost is less? Something like BRK.B vs BRK.A, or different funds that track the same, or essentially the same, underlying index or group of assets?
- Is there something special about X? Could you instead buy some unrelated asset Y each month?
If you're dead set on buying X:
- Buy every two or three months. While DCA is often specified as buying monthly, there's no rule that says you have to do that. People reinvesting dividends are buying every three months (typically).
- Buy as much as you can this month, saving what's left over (possibly the whole $1k) for next month. That may turn into effectively buying every two months with an occasional one month interval.
Also, a couple of things to keep in mind:
- How much commission are you paying and how good are your executions? If you're paying, say, $10 per trade and you're losing 1% because of slippage and/or buying at the ask and selling at the bid, that's 2%/month, which is a big headwind to overcome. That's probably high, but possible for low volumes.
- If you DCA 2 or 3 months, or even when you have enough money saved up, don't fall into the trap of trying to guess when the asset is down and when it's up. If your plan says buy every 3 months, buy every 3 months, regardless what X is doing (unless it's doing something that makes you think it's no longer a good investment of course).
Given the possibly high cost you might consider waiting until you can invest more per month, and for now just invest in a low cost mutual fund. For example, Vanguard index funds typically have very low expense ratios and those you can buy fractional shares of.
So yes, you can still DCA, but not on a strict $x/month cadence, but that's ok.