%% Plenty of them+ got cheaper.LOL Some of them have bigger bid/ask/spread............................
Have you considered trading SH? It's an inverse ETF, so you would have to flip your entries. But it's much cheaper than SPY, and it has decent liquidity.
%% Yes; VOO. [Vanguard]strangely always seems to be cheaper than SPY, maybe almost as liquid. But i have so many SPY charts; i go the other way, depends on OCT.........like trends.
SPY, IVV and VOO are all in the same price range. To average up or down during extended period of time, options also have a catch. SPY at 281. Call 282 Apr (1 month) cost 3.65 (1.3%) Call 282 Jun (3 months) cost 7.85 (2.8%) Call 282 Sep (6 months) cost 11.80 (4.2%) Time value (decay) can eat all the profit on an average strategy. For example, if 282 goes to 289.85 in June you're still break even. To minimize that you could go with deep ITM ones (less time value) but then something like Call 200 Sep has a bid/ask of 83.20/83.52. You're going to pay a lot in slippage to get in/out of the positions. The odd lots already suggested sound the simplest solution for what you want.
I think that you put a rather limiting constraint on yourself by demanding that you can not handle odd lots. How accurate does the ETF have to track the S&P500? If some tracking error is allowed you could consider to use VUG or VTV.
Coming May, we are supposed to get micro s&p futures. Every contract should be close to 50 shares of spy since it's 1/10th of ES.