I'd always assume the bill was going to be split and I would take my purse out as soon as the bill arrived. To be perfectly honest, I'm really uncomfortable being paid for.
However, there are some places I know I just couldn't afford for dinner on my current wage. If he suggested an expensive restaurant, especially for an early date, I'd have to be honest and say it was outside of my budget. If he insisted on going and said it was his treat then I would attend but I'd cover the drinks and/or say next date was on me.
I know a woman who is an exercise instructor and earns very little, just enough to cover her modest one bed flat and her dog. She had a man do a big plumbing job in her home over a few days and he seemed really lovely, respectful, kind etc. She was in her early 40s and had been single for a very long time and quite lonely. Long story short they ended up going on a coffee date which came to about £10 total. She offered to pay and he insisted making a huge grand gesture of paying. It had been a brilliant date and she felt so positive. He took her hand and told her what a lovely time he'd and for the next date he wanted to take her someplace really special and suggested a really upmarket restaurant. He insinuated it was his treat and said she deserved to go out someplace lovely and said she could get all dressed up etc.
At the end of that date the bill came to about £250. She waited for him to pay and he just stared at her. She said 'oh, are we splitting it?" and he said, "well I paid for the last date so it's your turn to pay." She thought he was joking and offered to pay half (even though she couldn't really afford half either) but he was adamant he wouldn't pay and said something along the lines of "Oh c'mon, I've had such a lovely time. Let's not ruin it by making me feel taken advantage of." She paid for the whole thing on an emergency credit card. She was so upset as I think she'd been thinking he could be the one up until then. The dinner cost more than her weekly wage I'd imagine.
Anyway, her story made me realise that I'd hate to be put in that situation too so that's why I'd a) never go anywhere outside of my budget on an early date and b) explain beforehand if I'd struggle to cover my half and suggest an alternative venue.